Thomas Devereaux
Professor of Photon Science and of Materials Science and Engineering
Photon Science Directorate
Bio
Professor Devereaux received his Ph.D. in Physics from the University of Oregon in 1991, M.S. from University of Oregon in 1988, and B.S from New York University in 1986.
Professor Devereaux is a professor in Materials Science & Engineering and Photon Science at SLAC National Accelerator Laboratory and Stanford University, and a Senior Fellow of the Precourt Institute for Energy. He was formerly the Director of the Stanford Institute for Materials and Energy Sciences (SIMES) from 2011-2020.
Professor Devereaux was a Post-doctoral Fellow at the Max Planck Institut, Stuttgart, (1991-1993), a Post-doctoral Fellow at the University of California, Davis, CA, (1993-1996), an Assistant Professor at The George Washington University, Washington, DC, (1996-1999), and an Associate Professor (1999-2006) and Professor (2006-2007) at the University of Waterloo, Waterloo, ON, Canada
His main research interests lie in the areas of theoretical condensed matter physics and computational physics. His research effort focuses on using the tools of computational physics to understand quantum materials. The goal of his research is to understand equilibrium and ultrafast non-equilibrium electron dynamics via a combination of analytical theory and numerical simulations to provide insight into materials of relevance to energy science. His group carries out numerical simulations on SIMES' high-performance compute cluster, the National Energy Research Scientific Computing Center (NERSC), and other US computational facilities. The specific focus of the group is the development of numerical methods and theories of photon-based spectroscopies of strongly correlated quantum materials and novel materials for energy storage.
Academic Appointments
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Professor, Photon Science Directorate
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Professor, Materials Science and Engineering
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Principal Investigator, Stanford Institute for Materials and Energy Sciences
Honors & Awards
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Fellowship, U. S. Department of Education (1989-1991)
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Junior Scholar Incentive Award, George Washington University (1998)
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Research Fellowship, Alexander von Humboldt Foundation (2002-2006)
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Premier's Research Excellence Award, Province of Ontario (2003)
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Scientist Research Fellowship, Embassy of France (2005 & 2006)
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Fellow, American Physical Society (2008)
Professional Education
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Ph.D., University of Oregon, Physics (1991)
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M.S., University of Oregon, Physics (1988)
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B.S., New York University, Mathematics & Physics (1986)
Current Research and Scholarly Interests
My main research interests lie in the areas of theoretical condensed matter physics and computational physics. My research effort focuses on using the tools of computational physics to understand quantum materials. Fortunately, we are poised in an excellent position as the speed and cost of computers have allowed us to tackle heretofore unaddressed problems involving interacting systems. The goal of my research is to understand electron dynamics via a combination of analytical theory and numerical simulations to provide insight into materials of relevance to energy science. My group carries out numerical simulations on SIMES’ high-performance supercomputer and US and Canadian computational facilities. The specific focus of my group is the development of numerical methods and theories of photon-based spectroscopies of strongly correlated materials.
2024-25 Courses
- Quantum Mechanics for Materials Science
MATSCI 185 (Win) - Quantum Mechanics for Materials Science
MATSCI 215 (Win) -
Independent Studies (8)
- Directed Studies in Applied Physics
APPPHYS 290 (Aut, Win, Spr, Sum) - Graduate Independent Study
MATSCI 399 (Aut, Win, Spr, Sum) - Independent Research and Study
PHYSICS 190 (Aut, Win, Spr, Sum) - Master's Research
MATSCI 200 (Aut, Win, Spr, Sum) - Ph.D. Research
MATSCI 300 (Aut, Win, Spr, Sum) - Practical Training
MATSCI 299 (Aut, Win, Spr, Sum) - Research
PHYSICS 490 (Aut, Win, Spr, Sum) - Undergraduate Research
MATSCI 150 (Aut, Win, Spr, Sum)
- Directed Studies in Applied Physics
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Prior Year Courses
2023-24 Courses
- Quantum Mechanics for Materials Science
MATSCI 185 (Win) - Quantum Mechanics for Materials Science
MATSCI 215 (Win)
2022-23 Courses
- Condensed Matter Seminar
APPPHYS 470 (Aut, Win, Spr) - Quantum Mechanics for Materials Science
MATSCI 185 (Win) - Quantum Mechanics for Materials Science
MATSCI 215 (Win) - Statistical Mechanics for Materials & Materials Chemistry
MATSCI 310 (Spr)
2021-22 Courses
- Condensed Matter Seminar
APPPHYS 470 (Aut, Win, Spr) - Quantum Mechanics for Materials Science
MATSCI 185 (Win) - Quantum Mechanics for Materials Science
MATSCI 215 (Win)
- Quantum Mechanics for Materials Science
Stanford Advisees
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Doctoral Dissertation Reader (AC)
Jay Qu, Hari Ramachandran -
Postdoctoral Faculty Sponsor
Shengtao Jiang, Chris Parzyck, Emily Zhang, Zoe Zhu -
Doctoral Dissertation Advisor (AC)
Emma Cuddy, Sean Hsu, Malhar Kute, Eder Lomeli, Rong Zhang, Sijia Zhao -
Doctoral Dissertation Advisor (NonAC)
Martin Gonzalez -
Doctoral Dissertation Co-Advisor (AC)
Vladimir Calvera -
Postdoctoral Research Mentor
Daniel Jost
All Publications
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Enhanced Pair-Density-Wave Vertices in a Bilayer Hubbard Model at Half Filling.
Physical review letters
2024; 133 (15): 156503
Abstract
Motivated by the pair-density-wave (PDW) state found in the one-dimensional Kondo-Heisenberg chain, we report on a determinant quantum Monte Carlo study of pair fields for a two-dimensional half-filled Hubbard layer coupled to an itinerant, noninteracting layer with one electron per site. In a specific range of interlayer hopping, the pairing vertex associated with PDW order becomes more attractive than that for uniform d-wave pairing, although both remain subdominant to the leading antiferromagnetic correlations at half filling. Our result sheds light on where one potentially may find a PDW state in such a model.
View details for DOI 10.1103/PhysRevLett.133.156503
View details for PubMedID 39454175
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Enhanced Pair-Density-Wave Vertices in a Bilayer Hubbard Model at Half Filling
PHYSICAL REVIEW LETTERS
2024; 133 (15)
View details for DOI 10.1103/PhysRevLett.133.156503
View details for Web of Science ID 001334502500005
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Influence of extended interactions on spin dynamics in one-dimensional cuprates
PHYSICAL REVIEW B
2024; 110 (16)
View details for DOI 10.1103/PhysRevB.110.165118
View details for Web of Science ID 001335671500007
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Predicting Reactivity and Passivation of Solid-State Battery Interfaces.
ACS applied materials & interfaces
2024
Abstract
In this work, we build a computationally inexpensive, data-driven model that utilizes atomistic structure information to predict the reactivity of interfaces between any candidate solid-state electrolyte material and a Li metal anode. This model is trained on data from ab initio molecular dynamics (AIMD) simulations of the time evolution of the solid electrolyte-Li metal interfaces for 67 different materials. Predicting the reactivity of solid-state interfaces with ab initio techniques remains an elusive challenge in materials discovery and informatics, and previous work on predicting interfacial compatibility of solid-state Li-ion electrolytes and Li metal anodes has focused mainly on thermodynamic convex hull calculations. Our framework involves training machine learning models on AIMD data, thereby capturing information on both kinetics and thermodynamics, and then leveraging these models to predict the reactivity of thousands of new candidates in the span of seconds, avoiding the need for additional weeks-long AIMD simulations. We identify over 300 new chemically stable and over 780 passivating solid electrolytes that are predicted to be thermodynamically unfavored. Our results indicate many potential solid-state electrolyte candidates have been incorrectly labeled unstable via purely thermodynamic approaches using density functional theory (DFT) energetics, and that the pool of promising, Li-stable solid-state electrolyte materials may be much larger than previously thought from screening efforts. To showcase the value of our approach, we highlight two borate materials that were identified by our model and confirmed by further AIMD calculations to likely be highly conductive and chemically stable with Li: LiB13C2 and LiB12PC.
View details for DOI 10.1021/acsami.4c06095
View details for PubMedID 39277815
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Molecular geometry specific Monte Carlo simulation of the efficacy of diamond crystal formation from diamondoids.
Communications chemistry
2024; 7 (1): 194
Abstract
Diamondoids are a class of organic molecules with the carbon skeletons isostructural to nano-diamond, and have been shown to be promising precursors for diamond formation. In this work, the formation of diamond crystals from various diamondoid molecule building blocks was studied using our developed molecular geometry specific Monte Carlo method. We maintained the internal carbon skeletons of the diamondoid molecules, and investigated how the carbon-carbon bonds form between diamondoid molecules and how efficient the process is to form diamond crystals. The simulations show that higher diamondoid molecules can produce structures closer to a diamond crystal compared with lower diamondoid molecules. Specifically, using higher diamondoid molecules, larger bulk diamond crystals are formed with fewer vacancies. The higher propensity of certain diamondoids to form diamond crystals reveals insights into the microscopic processes of diamond formation under high-pressure high-temperature conditions.
View details for DOI 10.1038/s42004-024-01261-9
View details for PubMedID 39218958
View details for PubMedCentralID PMC11366742
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Improving the creation of SiV centers in diamond via sub-μs pulsed annealing treatment.
Nature communications
2024; 15 (1): 7251
Abstract
Silicon-vacancy (SiV) centers in diamond are emerging as promising quantum emitters in applications such as quantum communication and quantum information processing. Here, we demonstrate a sub-μs pulsed annealing treatment that dramatically increases the photoluminescence of SiV centers in diamond. Using a silane-functionalized adamantane precursor and a laser-heated diamond anvil cell, the temperature and energy conditions required to form SiV centers in diamond were mapped out via an optical thermometry system with an accuracy of ±50 K and a 1 μs temporal resolution. Annealing scheme studies reveal that pulsed annealing can obviously minimize the migration of SiV centers out of the diamond lattice, and a 2.5-fold increase in the number of emitting centers was achieved using a series of 200-ns pulses at a 50 kHz repetition rate via acousto-optic modulation. Our study provides a novel pulsed annealing treatment approach to improve the efficiency of the creation of SiV centers in diamond.
View details for DOI 10.1038/s41467-024-51523-2
View details for PubMedID 39179592
View details for PubMedCentralID 7097076
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Anomalous normal-state gap in an electron-doped cuprate.
Science (New York, N.Y.)
2024; 385 (6710): 796-800
Abstract
In the underdoped n-type cuprate Nd2-xCexCuO4, long-range antiferromagnetic order reconstructs the Fermi surface, resulting in a putative antiferromagnetic metal with small Fermi pockets. Using angle-resolved photoemission spectroscopy, we observe an anomalous energy gap, an order of magnitude smaller than the antiferromagnetic gap, in a wide portion of the underdoped regime and smoothly connecting to the superconducting gap at optimal doping. After considering all the known ordering tendencies in tandem with the phase diagram, we hypothesize that the normal-state gap in the underdoped n-type cuprates originates from Cooper pairing. The high temperature scale of the normal-state gap raises the prospect of engineering higher transition temperatures in the n-type cuprates comparable to those of the p-type cuprates.
View details for DOI 10.1126/science.adk4792
View details for PubMedID 39146411
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Recovery of a Luther-Emery phase in the three-band Hubbard ladder with longer-range hopping
PHYSICAL REVIEW B
2024; 110 (1)
View details for DOI 10.1103/PhysRevB.110.014511
View details for Web of Science ID 001270519000002
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Emergence of antiferromagnetic correlations and Kondolike features in a model for infinite layer nickelates
NPJ QUANTUM MATERIALS
2024; 9 (1)
View details for DOI 10.1038/s41535-024-00659-x
View details for Web of Science ID 001243372200001
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Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal.
Nano letters
2024
Abstract
Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.
View details for DOI 10.1021/acs.nanolett.4c00758
View details for PubMedID 38717626
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Anharmonic strong-coupling effects at the origin of the charge density wave in CsV3Sb5.
Nature communications
2024; 15 (1): 1895
Abstract
The formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV3Sb5 using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with 2 Delta max / k B T CDW 20 , far beyond the prediction of mean-field theory. The analysis of the A1g and E2g phonons, including those emerging below TCDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A1g amplitude mode suggests strong electron-phonon coupling below TCDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV3Sb5.
View details for DOI 10.1038/s41467-024-45865-0
View details for PubMedID 38429269
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Ground-state phase diagram and superconductivity of the doped Hubbard model on six-leg square cylinders
PHYSICAL REVIEW B
2024; 109 (8)
View details for DOI 10.1103/PhysRevB.109.085121
View details for Web of Science ID 001199616100005
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Collective Nature of Orbital Excitations in Layered Cuprates in the Absence of Apical Oxygens.
Physical review letters
2024; 132 (6): 066004
Abstract
We have investigated the 3d orbital excitations in CaCuO_{2} (CCO), Nd_{2}CuO_{4} (NCO), and La_{2}CuO_{4} (LCO) using high-resolution resonant inelastic x-ray scattering. In LCO they behave as well-localized excitations, similarly to several other cuprates. On the contrary, in CCO and NCO the d_{xy} orbital clearly disperses, pointing to a collective character of this excitation (orbiton) in compounds without apical oxygen. We ascribe the origin of the dispersion as stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange. Such an exchange leads to the liberation of the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy.
View details for DOI 10.1103/PhysRevLett.132.066004
View details for PubMedID 38394564
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Charge order and superconductivity in a two-band model for infinite-layer nickelates
PHYSICAL REVIEW B
2023; 108 (24)
View details for DOI 10.1103/PhysRevB.108.245115
View details for Web of Science ID 001144917900008
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Bogoliubov quasiparticle on the gossamer Fermi surface in electron-doped cuprates
NATURE PHYSICS
2023; 19 (12): 1834-+
View details for DOI 10.1038/s41567-023-02209-x
View details for Web of Science ID 001178645300029
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The Wiedemann-Franz law in doped Mott insulators without quasiparticles.
Science (New York, N.Y.)
2023; 382 (6674): 1070-1073
Abstract
Many metallic quantum materials display anomalous transport phenomena that defy a Fermi liquid description. Here, we use numerical methods to calculate thermal and charge transport in the doped Hubbard model and observe a crossover separating high- and low-temperature behaviors. Distinct from the behavior at high temperatures, the Lorenz number [Formula: see text] becomes weakly doping dependent and less sensitive to parameters at low temperatures. At the lowest numerically accessible temperatures, [Formula: see text] roughly approaches the Wiedemann-Franz constant [Formula: see text], even in a doped Mott insulator that lacks well-defined quasiparticles. Decomposing the energy current operator indicates a compensation between kinetic and potential contributions, which may help to clarify the interpretation of transport experiments beyond Boltzmann theory in strongly correlated metals.
View details for DOI 10.1126/science.ade3232
View details for PubMedID 38033050
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Proximate spin liquid and fractionalization in the triangular antiferromagnet KYbSe<sub>2</sub>
NATURE PHYSICS
2023
View details for DOI 10.1038/s41567-023-02259-1
View details for Web of Science ID 001099033900001
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Quantitative assessment of the universal thermopower in the Hubbard model.
Nature communications
2023; 14 (1): 7064
Abstract
As primarily an electronic observable, the room-temperature thermopower S in cuprates provides possibilities for a quantitative assessment of the Hubbard model. Using determinant quantum Monte Carlo, we demonstrate agreement between Hubbard model calculations and experimentally measured room-temperature S across multiple cuprate families, both qualitatively in terms of the doping dependence and quantitatively in terms of magnitude. We observe an upturn in S with decreasing temperatures, which possesses a slope comparable to that observed experimentally in cuprates. From our calculations, the doping at which S changes sign occurs in close proximity to a vanishing temperature dependence of the chemical potential at fixed density. Our results emphasize the importance of interaction effects in the systematic assessment of the thermopower S in cuprates.
View details for DOI 10.1038/s41467-023-42772-8
View details for PubMedID 37923746
View details for PubMedCentralID PMC10624669
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Angle-resolved pair photoemission theory for correlated electrons
PHYSICAL REVIEW B
2023; 108 (6)
View details for DOI 10.1103/PhysRevB.108.165134
View details for Web of Science ID 001100593900005
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Bogoliubov quasiparticle on the gossamer Fermi surface in electron-doped cuprates
NATURE PHYSICS
2023
View details for DOI 10.1038/s41567-023-02209
View details for Web of Science ID 001071598400003
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Ingredients of strong interactions in cuprates
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS
2023; 613
View details for DOI 10.1016/j.physc.2023.1354356
View details for Web of Science ID 001084745200001
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From Stoner to local moment magnetism in atomically thin Cr2Te3.
Nature communications
2023; 14 (1): 5340
Abstract
The field of two-dimensional (2D) ferromagnetism has been proliferating over the past few years, with ongoing interests in basic science and potential applications in spintronic technology. However, a high-resolution spectroscopic study of the 2D ferromagnet is still lacking due to the small size and air sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent ferromagnetism in epitaxially grown Cr2Te3 thin films and investigate the evolution of the underlying electronic structure by synergistic angle-resolved photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption spectroscopy, and first-principle calculations. A conspicuous ferromagnetic transition from Stoner to Heisenberg-type is directly observed in the atomically thin limit, indicating that dimensionality is a powerful tuning knob to manipulate the novel properties of 2D magnetism. Monolayer Cr2Te3 retains robust ferromagnetism, but with a suppressed Curie temperature, due to the drastic drop in the density of states near the Fermi level. Our results establish atomically thin Cr2Te3 as an excellent platform to explore the dual nature of localized and itinerant ferromagnetism in 2D magnets.
View details for DOI 10.1038/s41467-023-40997-1
View details for PubMedID 37660171
View details for PubMedCentralID PMC10475109
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Publisher Correction: Geometric frustration of Jahn-Teller order in the infinite-layer lattice.
Nature
2023
View details for DOI 10.1038/s41586-023-06432-7
View details for PubMedID 37474799
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Traces of electron-phonon coupling in one-dimensional cuprates.
Nature communications
2023; 14 (1): 3129
Abstract
The appearance of certain spectral features in one-dimensional (1D) cuprate materials has been attributed to a strong, extended attractive coupling between electrons. Here, using time-dependent density matrix renormalization group methods on a Hubbard-extended Holstein model, we show that extended electron-phonon (e-ph) coupling presents an obvious choice to produce such an attractive interaction that reproduces the observed spectral features and doping dependence seen in angle-resolved photoemission experiments: diminished 3kF spectral weight, prominent spectral intensity of a holon-folding branch, and the correct holon band width. While extended e-ph coupling does not qualitatively alter the ground state of the 1D system compared to the Hubbard model, it quantitatively enhances the long-range superconducting correlations and suppresses spin correlations. Such an extended e-ph interaction may be an important missing ingredient in describing the physics of the structurally similar two-dimensional high-temperature superconducting layered cuprates, which may tip the balance between intertwined orders in favor of uniform d-wave superconductivity.
View details for DOI 10.1038/s41467-023-38408-6
View details for PubMedID 37253739
View details for PubMedCentralID PMC10229634
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Effects of rare-earth magnetism on the superconducting upper critical field in infinite-layer nickelates.
Science advances
2023; 9 (20): eadf6655
Abstract
The search for superconductivity in infinite-layer nickelates was motivated by analogy to the cuprates, and this perspective has framed much of the initial consideration of this material. However, a growing number of studies have highlighted the involvement of rare-earth orbitals; in that context, the consequences of varying the rare-earth element in the superconducting nickelates have been much debated. Here, we show notable differences in the magnitude and anisotropy of the superconducting upper critical field across the La-, Pr-, and Nd-nickelates. These distinctions originate from the 4f electron characteristics of the rare-earth ions in the lattice: They are absent for La3+, nonmagnetic for the Pr3+ singlet ground state, and magnetic for the Nd3+ Kramer's doublet. The unique polar and azimuthal angle-dependent magnetoresistance found in the Nd-nickelates can be understood to arise from the magnetic contribution of the Nd3+ 4f moments. Such robust and tunable superconductivity suggests potential in future high-field applications.
View details for DOI 10.1126/sciadv.adf6655
View details for PubMedID 37196089
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Enhanced superconductivity by near-neighbor attraction in the doped extended Hubbard model
PHYSICAL REVIEW B
2023; 107 (20)
View details for DOI 10.1103/PhysRevB.107.L201102
View details for Web of Science ID 000986820400004
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Reversal of spin-polarization near the Fermi level of the Rashba semiconductor BiTeCl
NPJ QUANTUM MATERIALS
2023; 8 (1)
View details for DOI 10.1038/s41535-023-00546-x
View details for Web of Science ID 000941936700001
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Signatures of the exciton gas phase and its condensation in monolayer 1T-ZrTe2.
Nature communications
2023; 14 (1): 1116
Abstract
The excitonic insulator (EI) is a Bose-Einstein condensation (BEC) of excitons bound by electron-hole interaction in a solid, which could support high-temperature BEC transition. The material realization of EI has been challenged by the difficulty of distinguishing it from a conventional charge density wave (CDW) state. In the BEC limit, the preformed exciton gas phase is a hallmark to distinguish EI from conventional CDW, yet direct experimental evidence has been lacking. Here we report a distinct correlated phase beyond the 2×2 CDW ground state emerging in monolayer 1T-ZrTe2 and its investigation by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The results show novel band- and energy-dependent folding behavior in a two-step process, which is the signatures of an exciton gas phase prior to its condensation into the final CDW state. Our findings provide a versatile two-dimensional platform that allows tuning of the excitonic effect.
View details for DOI 10.1038/s41467-023-36857-7
View details for PubMedID 36849499
View details for PubMedCentralID PMC9971207
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Geometric frustration of Jahn-Teller order in the infinite-layer lattice.
Nature
2023
Abstract
The Jahn-Teller effect, in which electronic configurations with energetically degenerate orbitals induce lattice distortions to lift this degeneracy, has a key role in many symmetry-lowering crystal deformations1. Lattices of Jahn-Teller ions can induce a cooperative distortion, as exemplified by LaMnO3 (refs. 2,3). Although many examples occur in octahedrally4 or tetrahedrally5 coordinated transition metal oxides due to their high orbital degeneracy, this effect has yet to be manifested for square-planar anion coordination, as found in infinite-layer copper6,7, nickel8,9, iron10,11 and manganese oxides12. Here we synthesize single-crystal CaCoO2 thin films by topotactic reduction of the brownmillerite CaCoO2.5 phase. We observe a markedly distorted infinite-layer structure, with angstrom-scale displacements of the cations from their high-symmetry positions. This can be understood to originate from the Jahn-Teller degeneracy of the dxz and dyz orbitals in the d7 electronic configuration along with substantial ligand-transition metal mixing. A complex pattern of distortions arises in a [Formula: see text] tetragonal supercell, reflecting the competition between an ordered Jahn-Teller effect on the CoO2 sublattice and the geometric frustration of the associated displacements of the Ca sublattice, which are strongly coupled in the absence of apical oxygen. As a result of this competition, the CaCoO2 structure forms an extended two-in-two-out type of Co distortion following 'ice rules'13.
View details for DOI 10.1038/s41586-022-05681-2
View details for PubMedID 36813969
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Fluctuating intertwined stripes in the strange metal regime of the Hubbard model br
PHYSICAL REVIEW B
2023; 107 (8)
View details for DOI 10.1103/PhysRevB.107.085126
View details for Web of Science ID 000975295600001
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Identification of a characteristic doping for charge order phenomena in Bi-2212 cuprates via RIXS
PHYSICAL REVIEW B
2022; 106 (15)
View details for DOI 10.1103/PhysRevB.106.155109
View details for Web of Science ID 000918192100003
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Spectra of a gapped quantum spin liquid with a strong chiral excitation on the triangular lattice
PHYSICAL REVIEW B
2022; 106 (6)
View details for DOI 10.1103/PhysRevB.106.064428
View details for Web of Science ID 000861306700001
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Thermodynamics of correlated electrons in a magnetic field
COMMUNICATIONS PHYSICS
2022; 5 (1)
View details for DOI 10.1038/s42005-022-00968-2
View details for Web of Science ID 000838678400003
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A broken translational symmetry state in an infinite-layer nickelate
NATURE PHYSICS
2022
View details for DOI 10.1038/s41567-022-01660-6
View details for Web of Science ID 000829739500004
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Electronic structure of superconducting nickelates probed by resonant photoemission spectroscopy
MATTER
2022; 5 (6)
View details for DOI 10.1016/j.matt.2022.01.020
View details for Web of Science ID 000810939100001
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Self-energy dynamics and the mode-specific phonon threshold effect in Kekule-ordered graphene.
National science review
2022; 9 (5): nwab175
Abstract
Electron-phonon interaction and related self-energy are fundamental to both the equilibrium properties and non-equilibrium relaxation dynamics of solids. Although electron-phonon interaction has been suggested by various time-resolved measurements to be important for the relaxation dynamics of graphene, the lack of energy- and momentum-resolved self-energy dynamics prohibits direct identification of the role of specific phonon modes in the relaxation dynamics. Here, by performing time- and angle-resolved photoemission spectroscopy measurements on Kekule-ordered graphene with folded Dirac cones at the Gamma point, we have succeeded in resolving the self-energy effect induced by the coupling of electrons to two phonons at Omega1 = 177 meV and Omega2 = 54 meV, and revealing its dynamical change in the time domain. Moreover, these strongly coupled phonons define energy thresholds, which separate the hierarchical relaxation dynamics from ultrafast, fast to slow, thereby providing direct experimental evidence for the dominant role of mode-specific phonons in the relaxation dynamics.
View details for DOI 10.1093/nsr/nwab175
View details for PubMedID 35663240
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Momentum-resolved resonant inelastic soft X-ray scattering (qRIXS) endstation at the ALS
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
2022; 257
View details for DOI 10.1016/j.elspec.2019.146897
View details for Web of Science ID 000816180900004
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Magnon heat transport in a two-dimensional Mott insulator
PHYSICAL REVIEW B
2022; 105 (16)
View details for DOI 10.1103/PhysRevB.105.L161103
View details for Web of Science ID 000832853800001
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Sign-free determinant quantum Monte Carlo study of excitonic density orders in a two-orbital Hubbard-Kanamori model
PHYSICAL REVIEW B
2022; 105 (16)
View details for DOI 10.1103/PhysRevB.105.165124
View details for Web of Science ID 000832850000002
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Anisotropy of the magnetic and transport properties of EuZn2As2
PHYSICAL REVIEW B
2022; 105 (16)
View details for DOI 10.1103/PhysRevB.105.165122
View details for Web of Science ID 000832845000002
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On the Nature of Valence Charge and Spin Excitations via Multi-Orbital Hubbard Models for Infinite-Layer Nickelates
FRONTIERS IN PHYSICS
2022; 10
View details for DOI 10.3389/fphy.2022.836959
View details for Web of Science ID 000776236900001
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Distinguishing finite-momentum superconducting pairing states with two-electron photoemission spectroscopy
PHYSICAL REVIEW B
2022; 105 (6)
View details for DOI 10.1103/PhysRevB.105.064515
View details for Web of Science ID 000766643200007
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Polarization-Modulated Angle-Resolved Photoemission Spectroscopy: Toward Circular Dichroism without Circular Photons and Bloch Wave-function Reconstruction
PHYSICAL REVIEW X
2022; 12 (1)
View details for DOI 10.1103/PhysRevX.12.011019
View details for Web of Science ID 000749381700001
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Unconventional spectral signature of Tc in a pure d-wave superconductor.
Nature
1800; 601 (7894): 562-567
Abstract
In conventional superconductors, the phase transition into a zero-resistance and perfectly diamagnetic state is accompanied by a jump in the specific heat and the opening of a spectral gap1. In the high-transition-temperature (high-Tc) cuprates, although the transport, magnetic and thermodynamic signatures of Tc have been known since the 1980s2, the spectroscopic singularity associated with the transition remains unknown. Here we resolve this long-standing puzzle with a high-precision angle-resolved photoemission spectroscopy (ARPES) study on overdoped (Bi,Pb)2Sr2CaCu2O8+delta (Bi2212). We first probe the momentum-resolved electronic specific heat via spectroscopy and reproduce the specific heat peak at Tc, completing the missing link for a holistic description of superconductivity. Then, by studying the full momentum, energy and temperature evolution of the spectra, we reveal that this thermodynamic anomaly arises from the singular growth of in-gap spectral intensity across Tc. Furthermore, we observe that the temperature evolution of in-gap intensity is highly anisotropic in the momentum space, and the gap itself obeys both the d-wave functional form and particle-hole symmetry. These findings support the scenario that the superconducting transition is driven by phase fluctuations. They also serve as an anchor point for understanding the Fermi arc and pseudogap phenomena in underdoped cuprates.
View details for DOI 10.1038/s41586-021-04251-2
View details for PubMedID 35082417
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Web-based methods for X-ray and photoelectron spectroscopies
COMPUTATIONAL MATERIALS SCIENCE
2021; 200
View details for DOI 10.1016/j.commatsci.2021.110814
View details for Web of Science ID 000704339800009
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Orbitally selective resonant photodoping to enhance superconductivity
PHYSICAL REVIEW B
2021; 104 (17)
View details for DOI 10.1103/PhysRevB.104.174516
View details for Web of Science ID 000722738700004
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Intertwined States at Finite Temperatures in the Hubbard Model
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
2021; 90 (11)
View details for DOI 10.7566/JPSJ.90.111010
View details for Web of Science ID 000706633300001
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Phonon-Mediated Long-Range Attractive Interaction in One-Dimensional Cuprates
PHYSICAL REVIEW LETTERS
2021; 127 (19): 197003
Abstract
Establishing a minimal microscopic model for cuprates is a key step towards the elucidation of a high-T_{c} mechanism. By a quantitative comparison with a recent in situ angle-resolved photoemission spectroscopy measurement in doped 1D cuprate chains, our simulation identifies a crucial contribution from long-range electron-phonon coupling beyond standard Hubbard models. Using reasonable ranges of coupling strengths and phonon energies, we obtain a strong attractive interaction between neighboring electrons, whose strength is comparable to experimental observations. Nonlocal couplings play a significant role in the mediation of neighboring interactions. Considering the structural and chemical similarity between 1D and 2D cuprate materials, this minimal model with long-range electron-phonon coupling will provide important new insights on cuprate high-T_{c} superconductivity and related quantum phases.
View details for DOI 10.1103/PhysRevLett.127.197003
View details for Web of Science ID 000717968300004
View details for PubMedID 34797146
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Superconducting Fluctuations in Overdoped Bi2Sr2CaCu2O8+delta
PHYSICAL REVIEW X
2021; 11 (3)
View details for DOI 10.1103/PhysRevX.11.031068
View details for Web of Science ID 000704695200001
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X-ray scattering from light-driven spin fluctuations in a doped Mott insulator
COMMUNICATIONS PHYSICS
2021; 4 (1)
View details for DOI 10.1038/s42005-021-00715-z
View details for Web of Science ID 000698400300002
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Numerical approaches for calculating the low-field dc Hall coefficient of the doped Hubbard model
PHYSICAL REVIEW RESEARCH
2021; 3 (3)
View details for DOI 10.1103/PhysRevResearch.3.033033
View details for Web of Science ID 000671591900001
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Precursor of pair-density wave in doping Kitaev spin liquid on the honeycomb lattice
NPJ QUANTUM MATERIALS
2021; 6 (1)
View details for DOI 10.1038/s41535-021-00363-0
View details for Web of Science ID 000669205300001
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Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox
ENERGY & ENVIRONMENTAL SCIENCE
2021
View details for DOI 10.1039/d1ee01037a
View details for Web of Science ID 000671934700001
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Evolution of the electronic structure in Ta2NiSe5 across the structural transition revealed by resonant inelastic x-ray scattering
PHYSICAL REVIEW B
2021; 103 (23)
View details for DOI 10.1103/PhysRevB.103.235159
View details for Web of Science ID 000668993500001
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Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates.
Advanced science (Weinheim, Baden-Wurttemberg, Germany)
2021; 8 (9): 2003454
Abstract
The enhanced superconductivity in monolayer FeSe on titanates opens a fascinating pathway toward the rational design of high-temperature superconductors. Utilizing the state-of-the-art oxide plus chalcogenide molecular beam epitaxy systems in situ connected to a synchrotron angle-resolved photoemission spectroscope, epitaxial LaTiO3 layers with varied atomic thicknesses are inserted between monolayer FeSe and SrTiO3, for systematic modulation of interfacial chemical potential. With the dramatic increase of electron accumulation at the LaTiO3/SrTiO3 surface, providing a substantial surge of work function mismatch across the FeSe/oxide interface, the charge transfer and the superconducting gap in the monolayer FeSe are found to remain markedly robust. This unexpected finding indicate the existence of an intrinsically anchored "magic" doping within the monolayer FeSe systems.
View details for DOI 10.1002/advs.202003454
View details for PubMedID 33977049
View details for PubMedCentralID PMC8097367
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Cycling mechanism of Li2MnO3: Li-CO2 batteries and commonality on oxygen redox in cathode materials
JOULE
2021; 5 (4): 975-997
View details for DOI 10.1016/j.joule.2021.02.004
View details for Web of Science ID 000642473100022
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Gauge invariance of light-matter interactions in first-principle tight-binding models
PHYSICAL REVIEW B
2021; 103 (15)
View details for DOI 10.1103/PhysRevB.103.155409
View details for Web of Science ID 000646756500004
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Tendencies of enhanced electronic nematicity in the Hubbard model and a comparison with Raman scattering on high-temperature superconductors
PHYSICAL REVIEW B
2021; 103 (13)
View details for DOI 10.1103/PhysRevB.103.134502
View details for Web of Science ID 000646193600004
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Electronic Structure Trends Across the Rare-Earth Series in Superconducting Infinite-Layer Nickelates
PHYSICAL REVIEW X
2021; 11 (1)
View details for DOI 10.1103/PhysRevX.11.011050
View details for Web of Science ID 000627595600002
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Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates
ADVANCED SCIENCE
2021
View details for DOI 10.1002/advs.202003454
View details for Web of Science ID 000617867700001
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Spectral properties and enhanced superconductivity in renormalized Migdal-Eliashberg theory
PHYSICAL REVIEW B
2021; 103 (2)
View details for DOI 10.1103/PhysRevB.103.024520
View details for Web of Science ID 000609012600006
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Preserving a robust CsPbI3 perovskite phase via pressure-directed octahedral tilt.
Nature communications
2021; 12 (1): 461
Abstract
Functional CsPbI3 perovskite phases are not stable at ambient conditions and spontaneously convert to a non-perovskite δ phase, limiting their applications as solar cell materials. We demonstrate the preservation of a black CsPbI3 perovskite structure to room temperature by subjecting the δ phase to pressures of 0.1 - 0.6 GPa followed by heating and rapid cooling. Synchrotron X-ray diffraction and Raman spectroscopy indicate that this perovskite phase is consistent with orthorhombic γ-CsPbI3. Once formed, γ-CsPbI3 could be then retained after releasing pressure to ambient conditions and shows substantial stability at 35% relative humidity. First-principles density functional theory calculations indicate that compression directs the out-of-phase and in-phase tilt between the [PbI6]4- octahedra which in turn tune the energy difference between δ- and γ-CsPbI3, leading to the preservation of γ-CsPbI3. Here, we present a high-pressure strategy for manipulating the (meta)stability of halide perovskites for the synthesis of desirable phases with enhanced materials functionality.
View details for DOI 10.1038/s41467-020-20745-5
View details for PubMedID 33469021
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Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox.
Energy & environmental science
2021; 14 (9)
Abstract
Stabilizing high-valent redox couples and exotic electronic states necessitate an understanding of the stabilization mechanism. In oxides, whether they are being considered for energy storage or computing, highly oxidized oxide-anion species rehybridize to form short covalent bonds and are related to significant local structural distortions. In intercalation oxide electrodes for batteries, while such reorganization partially stabilizes oxygen redox, it also gives rise to substantial hysteresis. In this work, we investigate oxygen redox in layered Na2-XMn3O7, a positive electrode material with ordered Mn vacancies. We prove that coulombic interactions between oxidized oxideanions and the interlayer Na vacancies can disfavor rehybridization and stabilize hole polarons on oxygen (O-) at 4.2 V vs. Na/Na+. These coulombic interactions provide thermodynamic energy saving as large as O-O covalent bonding and enable ~ 40 mV voltage hysteresis over multiple electrochemical cycles with negligible voltage fade. Our results establish a complete picture of redox energetics by highlighting the role of coulombic interactions across several atomic distances and suggest avenues to stabilize highly oxidized oxygen for applications in energy storage and beyond.
View details for DOI 10.1039/d1ee01037a
View details for PubMedID 37719447
View details for PubMedCentralID PMC10502899
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Dynamical signatures of symmetry protected topology following symmetry breaking
Physical Review Research
2021; 3 (2)
View details for DOI 10.1103/PhysRevResearch.3.023137
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Anomalously strong near-neighbor attraction in doped 1D cuprate chains.
Science (New York, N.Y.)
2021; 373 (6560): 1235-1239
Abstract
[Figure: see text].
View details for DOI 10.1126/science.abf5174
View details for PubMedID 34516788
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Correlation-Assisted Quantized Charge Pumping
Physical Review B
2021; 103 (3): 035112
View details for DOI 10.1103/PhysRevB.103.035112
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Time-resolved RIXS experiment with pulse-by-pulse parallel readout data collection using X-ray free electron laser.
Scientific reports
2020; 10 (1): 22226
Abstract
Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL). It is important to evaluate how the FEL jitter, which is inherent in the self-amplified spontaneous emission process, influences the RIXS measurement. Here, we use a microchannel plate (MCP) based Timepix softX-ray detector to conduct a time-resolved RIXS measurement at the Ti L3-edge on a charge-density-wave material TiSe2. The fast parallel Timepix readout and single photon sensitivity enable pulse-by-pulse data acquisition and analysis. Due to the FEL jitter, low detection efficiency of spectrometer, and low quantum yield of RIXS process, we find that less than 2% of the X-ray FEL pulses produce signals, preventing acquiring sufficient data statistics while maintaining temporal and energy resolution in this measurement. These limitations can be mitigated by using future X-ray FELs with high repetition rates, approaching MHz such as the European XFEL in Germany and LCLS-II in the USA, as well as by utilizing advanced detectors, such as the prototype used in this study.
View details for DOI 10.1038/s41598-020-79210-4
View details for PubMedID 33335197
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Site-specific structure at multiple length scales in kagome quantum spin liquid candidates
PHYSICAL REVIEW MATERIALS
2020; 4 (12)
View details for DOI 10.1103/PhysRevMaterials.4.124406
View details for Web of Science ID 000600660300004
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Emergence of quasiparticles in a doped Mott insulator
COMMUNICATIONS PHYSICS
2020; 3 (1)
View details for DOI 10.1038/s42005-020-00480-5
View details for Web of Science ID 000594380600003
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Observing photo-induced chiral edge states of graphene nanoribbons in pump-probe spectroscopies
NPJ QUANTUM MATERIALS
2020; 5 (1)
View details for DOI 10.1038/s41535-020-00283-5
View details for Web of Science ID 000588697200001
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How Circular Dichroism in Time- and Angle-Resolved Photoemission Can Be Used to Spectroscopically Detect Transient Topological States in Graphene
PHYSICAL REVIEW X
2020; 10 (4)
View details for DOI 10.1103/PhysRevX.10.041013
View details for Web of Science ID 000579342600001
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Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate (Aug, 10.1038/s41567-020-0993-7, 2020)
NATURE PHYSICS
2020
View details for DOI 10.1038/s41567-020-01075-1
View details for Web of Science ID 000578419100001
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Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate
NATURE PHYSICS
2020
View details for DOI 10.1038/s41567-020-0993-7
View details for Web of Science ID 000564497300003
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DC Hall coefficient of the strongly correlated Hubbard model
NPJ QUANTUM MATERIALS
2020; 5 (1)
View details for DOI 10.1038/s41535-020-00254-w
View details for Web of Science ID 000555945900002
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Ground state phase diagram of the doped Hubbard model on the four-leg cylinder
PHYSICAL REVIEW RESEARCH
2020; 2 (3)
View details for DOI 10.1103/PhysRevResearch.2.033073
View details for Web of Science ID 000604139800002
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Berry curvature memory through electrically driven stacking transitions
NATURE PHYSICS
2020
View details for DOI 10.1038/s41567-020-0947-0
View details for Web of Science ID 000544166500001
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Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb2.
Proceedings of the National Academy of Sciences of the United States of America
2020
Abstract
The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6 has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6 and YbB12 may also exist in systems with d instead of f electrons.
View details for DOI 10.1073/pnas.2002361117
View details for PubMedID 32571928
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Time-resolved resonant inelastic x-ray scattering in a pumped Mott insulator
PHYSICAL REVIEW B
2020; 101 (16)
View details for DOI 10.1103/PhysRevB.101.165126
View details for Web of Science ID 000527122300004
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Ab initio molecular dynamics study of SiO2 lithiation
CHEMICAL PHYSICS LETTERS
2020; 739
View details for DOI 10.1016/j.cplett.2019.136933
View details for Web of Science ID 000507233300103
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Site-Specific Structure at Multiple Length Scales in Kagome Quantum Spin Liquid Candidates.
Physical review materials
2020; 4 (12)
Abstract
Realizing a quantum spin liquid (QSL) ground state in a real material is a leading issue in condensed matter physics research. In this pursuit, it is crucial to fully characterize the structure and influence of defects, as these can significantly affect the fragile QSL physics. Here, we perform a variety of cutting-edge synchrotron X-ray scattering and spectroscopy techniques, and we advance new methodologies for site-specific diffraction and L-edge Zn absorption spectroscopy. The experimental results along with our first-principles calculations address outstanding questions about the local and long-range structures of the two leading kagome QSL candidates, Zn-substituted barlowite (Cu3Zn x Cu1-x (OH)6FBr) and herbertsmithite (Cu3Zn(OH)6Cl2). On all length scales probed, there is no evidence that Zn substitutes onto the kagome layers, thereby preserving the QSL physics of the kagome lattice. Our calculations show that antisite disorder is not energetically favorable and is even less favorable in Zn-barlowite compared to herbertsmithite. Site-specific X-ray diffraction measurements of Zn-barlowite reveal that Cu2+ and Zn2+ selectively occupy distinct interlayer sites, in contrast to herbertsmithite. Using the first measured Zn L-edge inelastic X-ray absorption spectra combined with calculations, we discover a systematic correlation between the loss of inversion symmetry from pseudo-octahedral (herbertsmithite) to trigonal prismatic coordination (Zn-barlowite) with the emergence of a new peak. Overall, our measurements suggest that Zn-barlowite has structural advantages over herbertsmithite that make its magnetic properties closer to an ideal QSL candidate: its kagome layers are highly resistant to nonmagnetic defects while the interlayers can accommodate a higher amount of Zn substitution.
View details for DOI 10.1103/physrevmaterials.4.124406
View details for PubMedID 34095744
View details for PubMedCentralID PMC8174140
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Biexciton Condensation in Electron-Hole-Doped Hubbard Bilayers: A Sign-Problem-Free Quantum Monte Carlo Study.
Physical review letters
2020; 124 (7): 077601
Abstract
The bilayer Hubbard model with electron-hole doping is an ideal platform to study excitonic orders due to suppressed recombination via spatial separation of electrons and holes. However, suffering from the sign problem, previous quantum Monte Carlo studies could not arrive at an unequivocal conclusion regarding the presence of phases with clear signatures of excitonic condensation in bilayer Hubbard models. Here, we develop a determinant quantum Monte Carlo algorithm for the bilayer Hubbard model that is sign-problem-free for equal and opposite doping in the two layers and study excitonic order and charge and spin density modulations as a function of chemical potential difference between the two layers, on-site Coulomb repulsion, and interlayer interaction. In the intermediate coupling regime and in proximity to the SU(4)-symmetric point, we find a biexcitonic condensate phase at finite electron-hole doping, as well as a competing (π,π) charge density wave state. We extract the Berezinskii-Kosterlitz-Thouless transition temperature from superfluid density and a finite-size scaling analysis of the correlation functions and explain our results in terms of an effective biexcitonic hard-core boson model.
View details for DOI 10.1103/PhysRevLett.124.077601
View details for PubMedID 32142325
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Facile diamond synthesis from lower diamondoids.
Science advances
2020; 6 (8): eaay9405
Abstract
Carbon-based nanomaterials have exceptional properties that make them attractive for a variety of technological applications. Here, we report on the use of diamondoids (diamond-like, saturated hydrocarbons) as promising precursors for laser-induced high-pressure, high-temperature diamond synthesis. The lowest pressure and temperature (P-T) conditions that yielded diamond were 12 GPa (at ~2000 K) and 900 K (at ~20 GPa), respectively. This represents a substantially reduced transformation barrier compared with diamond synthesis from conventional (hydro)carbon allotropes, owing to the similarities in the structure and full sp3 hybridization of diamondoids and bulk diamond. At 20 GPa, diamondoid-to-diamond conversion occurs rapidly within <19 μs. Molecular dynamics simulations indicate that once dehydrogenated, the remaining diamondoid carbon cages reconstruct themselves into diamond-like structures at high P-T. This study is the first successful mapping of the P-T conditions and onset timing of the diamondoid-to-diamond conversion and elucidates the physical and chemical factors that facilitate diamond synthesis.
View details for DOI 10.1126/sciadv.aay9405
View details for PubMedID 32128417
View details for PubMedCentralID PMC7034983
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The role of metal substitution in tuning anion redox in sodium metal layered oxides revealed by X-ray spectroscopy and theory.
Angewandte Chemie (International ed. in English)
2020
Abstract
We investigate high-valent oxygen redox in the positive Na-ion electrode P2-Na 0.67-x [Fe 0.5 Mn 0.5 ]O 2 (NMF) where Fe is partially substituted with Cu (P2-Na 0.67-x [Mn 0.66 Fe 0.20 Cu 0.14 ]O 2 , NMFC) or Ni (P2-Na 0.67-x [Mn 0.65 Fe 0.20 Ni 0.15 ]O 2 , NMFN). From combined analysis of resonant inelastic X-ray scattering and X-ray near-edge structure with electrochemical voltage hysteresis and X-ray pair distribution function profiles, we correlate structural disorder with high-valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A-O-A' local configuration in the pristine materials (where A= Na and A'= Li, Mg, vacancy, etc.). We also show that the Jahn-Teller nature of Fe 4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na-ion batteries.
View details for DOI 10.1002/anie.202012205
View details for PubMedID 33320987
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Angle-resolved photoemission spectroscopy of a Fermi-Hubbard system
NATURE PHYSICS
2020; 16 (1): 26-+
View details for DOI 10.1038/s41567-019-0696-0
View details for Web of Science ID 000508800600012
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Strange metallicity in the doped Hubbard model.
Science (New York, N.Y.)
2019; 366 (6468): 987–90
Abstract
Strange or bad metallic transport, defined by incompatibility with the conventional quasiparticle picture, is a theme common to many strongly correlated materials, including high-temperature superconductors. The Hubbard model represents a minimal starting point for modeling strongly correlated systems. Here we demonstrate strange metallic transport in the doped two-dimensional Hubbard model using determinantal quantum Monte Carlo calculations. Over a wide range of doping, we observe resistivities exceeding the Mott-Ioffe-Regel limit with linear temperature dependence. The temperatures of our calculations extend to as low as 1/40 of the noninteracting bandwidth, placing our findings in the degenerate regime relevant to experimental observations of strange metallicity. Our results provide a foundation for connecting theories of strange metals to models of strongly correlated materials.
View details for DOI 10.1126/science.aau7063
View details for PubMedID 31753997
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Field-induced quantum spin liquid in the Kitaev-Heisenberg model and its relation to alpha-RuCl3
PHYSICAL REVIEW B
2019; 100 (16)
View details for DOI 10.1103/PhysRevB.100.165123
View details for Web of Science ID 000490169800002
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Numerical investigation of spin excitations in a doped spin chain
PHYSICAL REVIEW B
2019; 99 (20)
View details for DOI 10.1103/PhysRevB.99.205102
View details for Web of Science ID 000466411400003
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Theory for time-resolved resonant inelastic x-ray scattering
PHYSICAL REVIEW B
2019; 99 (10)
View details for DOI 10.1103/PhysRevB.99.104306
View details for Web of Science ID 000462889500004
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Solid Electrolyte Interphase on Native Oxide-Terminated Silicon Anodes for Li-Ion Batteries
JOULE
2019; 3 (3): 762–81
View details for DOI 10.1016/j.joule.2018.12.013
View details for Web of Science ID 000462010600014
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Frustrated magnetism from local moments in FeSe
PHYSICAL REVIEW B
2019; 99 (12)
View details for DOI 10.1103/PhysRevB.99.125130
View details for Web of Science ID 000461963800010
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Fermi surface reconstruction in electron-doped cuprates without antiferromagnetic long-range order.
Proceedings of the National Academy of Sciences of the United States of America
2019; 116 (9): 3449–53
Abstract
Fermi surface (FS) topology is a fundamental property of metals and superconductors. In electron-doped cuprate Nd2-x Ce x CuO4 (NCCO), an unexpected FS reconstruction has been observed in optimal- and overdoped regime (x = 0.15-0.17) by quantum oscillation measurements (QOM). This is all the more puzzling because neutron scattering suggests that the antiferromagnetic (AFM) long-range order, which is believed to reconstruct the FS, vanishes before x = 0.14. To reconcile the conflict, a widely discussed external magnetic-field-induced AFM long-range order in QOM explains the FS reconstruction as an extrinsic property. Here, we report angle-resolved photoemission (ARPES) evidence of FS reconstruction in optimal- and overdoped NCCO. The observed FSs are in quantitative agreement with QOM, suggesting an intrinsic FS reconstruction without field. This reconstructed FS, despite its importance as a basis to understand electron-doped cuprates, cannot be explained under the traditional scheme. Furthermore, the energy gap of the reconstruction decreases rapidly near x = 0.17 like an order parameter, echoing the quantum critical doping in transport. The totality of the data points to a mysterious order between x = 0.14 and 0.17, whose appearance favors the FS reconstruction and disappearance defines the quantum critical doping. A recent topological proposal provides an ansatz for its origin.
View details for PubMedID 30808739
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Fermi surface reconstruction in electron-doped cuprates without antiferromagnetic long-range order
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2019; 116 (9): 3449–53
View details for DOI 10.1073/pnas.1816121116
View details for Web of Science ID 000459694400024
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Superconductivity in the doped Hubbard model and its interplay with next-nearest hopping t'.
Science (New York, N.Y.)
2019; 365 (6460): 1424–28
Abstract
The Hubbard model is widely believed to contain the essential ingredients of high-temperature superconductivity. However, proving definitively that the model supports superconductivity is challenging. Here, we report a large-scale density matrix renormalization group study of the lightly doped Hubbard model on four-leg cylinders at hole doping concentration δ = 12.5%. We reveal a delicate interplay between superconductivity and charge density wave and spin density wave orders tunable via next-nearest neighbor hopping t'. For finite t', the ground state is consistent with a Luther-Emery liquid with power-law superconducting and charge density wave correlations associated with half-filled charge stripes. In contrast, for t' = 0, superconducting correlations fall off exponentially, whereas charge density and spin density modulations are dominant. Our results indicate that a route to robust long-range superconductivity involves destabilizing insulating charge stripes in the doped Hubbard model.
View details for DOI 10.1126/science.aal5304
View details for PubMedID 31604270
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THz-Pump UED-Probe on a Topological Weyl Semimetal
IEEE. 2019
View details for Web of Science ID 000482226301297
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An Ultrafast Symmetry Switch in a Weyl Semimetal
Nature
2019; 565, 61
View details for DOI 10.1038/s41586-018-0809-4
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An ultrafast symmetry switch in a Weyl semimetal.
Nature
2019; 565 (7737): 61–66
Abstract
Topological quantum materials exhibit fascinating properties1-3, with important applications for dissipationless electronics and fault-tolerant quantum computers4,5. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors6. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron-ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend7-9. However, conventional means of applying strain through heteroepitaxial lattice mismatch10 and dislocations11 are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.
View details for PubMedID 30602749
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Incoherent strange metal sharply bounded by a critical doping in Bi2212.
Science (New York, N.Y.)
2019; 366 (6469): 1099–1102
Abstract
In normal metals, macroscopic properties are understood using the concept of quasiparticles. In the cuprate high-temperature superconductors, the metallic state above the highest transition temperature is anomalous and is known as the "strange metal." We studied this state using angle-resolved photoemission spectroscopy. With increasing doping across a temperature-independent critical value pc ~ 0.19, we observed that near the Brillouin zone boundary, the strange metal, characterized by an incoherent spectral function, abruptly reconstructs into a more conventional metal with quasiparticles. Above the temperature of superconducting fluctuations, we found that the pseudogap also discontinuously collapses at the very same value of pc These observations suggest that the incoherent strange metal is a distinct state and a prerequisite for the pseudogap; such findings are incompatible with existing pseudogap quantum critical point scenarios.
View details for DOI 10.1126/science.aaw8850
View details for PubMedID 31780552
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Theory of time-resolved Raman scattering in correlated systems: Ultrafast engineering of spin dynamics and detection of thermalization
PHYSICAL REVIEW B
2018; 98 (24)
View details for DOI 10.1103/PhysRevB.98.245106
View details for Web of Science ID 000452007800003
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Spectroscopic Signature of Oxidized Oxygen States in Peroxides
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
2018; 9 (21): 6378–84
View details for DOI 10.1021/acs.jpclett.8b02757
View details for Web of Science ID 000449308200032
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Spectroscopic Signature of Oxidized Oxygen States in Peroxides.
The journal of physical chemistry letters
2018: 6378–84
Abstract
Recent debates on the oxygen redox behaviors in battery electrodes have triggered a pressing demand for the reliable detection and understanding of nondivalent oxygen states beyond conventional absorption spectroscopy. Here, enabled by high-efficiency mapping of resonant inelastic X-ray scattering (mRIXS) coupled with first-principles calculations, we report distinct mRIXS features of the oxygen states in Li2O, Li2CO3, and especially, Li2O2, which are successfully reproduced and interpreted theoretically. mRIXS signals are dominated by valence-band decays in Li2O and Li2CO3. However, the oxidized oxygen in Li2O2 leads to partially unoccupied O-2p states that yield a specific intraband excitonic feature in mRIXS. Such a feature displays a specific emission energy in mRIXS, which disentangles the oxidized oxygen states from the dominating transition-metal/oxygen hybridization features in absorption spectroscopy, thus providing critical hints for both detecting and understanding the oxygen redox reactions in transition-metal oxide based battery materials.
View details for PubMedID 30354171
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Microscopic origin of Cooper pairing in the iron-based superconductor Ba1-xKxFe2As2
NPJ QUANTUM MATERIALS
2018; 3
View details for DOI 10.1038/s41535-018-0118-z
View details for Web of Science ID 000449705900001
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Anionic and cationic redox and interfaces in batteries: Advances from soft X-ray absorption spectroscopy to resonant inelastic scattering
JOURNAL OF POWER SOURCES
2018; 389: 188–97
View details for DOI 10.1016/j.jpowsour.2018.04.018
View details for Web of Science ID 000433267100022
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Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model.
Physical review letters
2018; 120 (24): 246401
Abstract
Understanding spin excitations and their connection to unconventional superconductivity have remained central issues since the discovery of cuprates. Direct measurement of the dynamical spin structure factor in the parent compounds can provide key information on important interactions relevant in the doped regime, and variations in the magnon dispersion have been linked closely to differences in crystal structure between families of cuprate compounds. Here, we elucidate the relationship between spin excitations and various controlling factors thought to be significant in high-T_{c} materials by systematically evaluating the dynamical spin structure factor for the three-orbital Hubbard model, revealing differences in the spin dispersion along the Brillouin zone axis and the diagonal. Generally, we find that the absolute energy scale and momentum dependence of the excitations primarily are sensitive to the effective charge-transfer energy, while changes in the on-site Coulomb interactions have little effect on the details of the dispersion. In particular, our result highlights the splitting between spin excitations along the axial and diagonal directions in the Brillouin zone. This splitting decreases with increasing charge-transfer energy and correlates with changes in the apical oxygen position, and general structural variations, for different cuprate families.
View details for DOI 10.1103/PhysRevLett.120.246401
View details for PubMedID 29956982
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Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model
PHYSICAL REVIEW LETTERS
2018; 120 (24)
View details for DOI 10.1103/PhysRevLett.120.246401
View details for Web of Science ID 000434766600010
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Unconventional pairing symmetry of interacting Dirac fermions on a pi-flux lattice
PHYSICAL REVIEW B
2018; 97 (15)
View details for DOI 10.1103/PhysRevB.97.155146
View details for Web of Science ID 000430459400003
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Influence of magnetism and correlation on the spectral properties of doped Mott insulators
PHYSICAL REVIEW B
2018; 97 (11)
View details for DOI 10.1103/PhysRevB.97.115120
View details for Web of Science ID 000427112600001
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Polaronic behavior in a weak-coupling superconductor
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2018; 115 (7): 1475–80
Abstract
The nature of superconductivity in the dilute semiconductor SrTiO3 has remained an open question for more than 50 y. The extremely low carrier densities ([Formula: see text]-[Formula: see text] cm-3) at which superconductivity occurs suggest an unconventional origin of superconductivity outside of the adiabatic limit on which the Bardeen-Cooper-Schrieffer (BCS) and Migdal-Eliashberg (ME) theories are based. We take advantage of a newly developed method for engineering band alignments at oxide interfaces and access the electronic structure of Nb-doped SrTiO3, using high-resolution tunneling spectroscopy. We observe strong coupling to the highest-energy longitudinal optic (LO) phonon branch and estimate the doping evolution of the dimensionless electron-phonon interaction strength ([Formula: see text]). Upon cooling below the superconducting transition temperature ([Formula: see text]), we observe a single superconducting gap corresponding to the weak-coupling limit of BCS theory, indicating an order of magnitude smaller coupling ([Formula: see text]). These results suggest that despite the strong normal state interaction with electrons, the highest LO phonon does not provide a dominant contribution to pairing. They further demonstrate that SrTiO3 is an ideal system to probe superconductivity over a wide range of carrier density, adiabatic parameter, and electron-phonon coupling strength.
View details for PubMedID 29382769
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Emergence of Interfacial Polarons from Electron-Phonon Coupling in Graphene/h-BN van der Waals Heterostructures
NANO LETTERS
2018; 18 (2): 1082–87
Abstract
van der Waals heterostructures, vertical stacks of layered materials, offer new opportunities for novel quantum phenomena which are absent in their constituent components. Here we report the emergence of polaron quasiparticles at the interface of graphene/hexagonal boron nitride (h-BN) heterostructures. Using nanospot angle-resolved photoemission spectroscopy, we observe zone-corner replicas of h-BN valence band maxima, with energy spacing coincident with the highest phonon energy of the heterostructure, an indication of Fröhlich polaron formation due to forward-scattering electron-phonon coupling. Parabolic fitting of the h-BN bands yields an effective mass enhancement of ∼2.3, suggesting an intermediate coupling strength. Our theoretical simulations based on Migdal-Eliashberg theory corroborate the experimental results, allowing the extraction of microscopic physical parameters. Moreover, renormalization of graphene π-band is observed due to the hybridization with the h-BN band. Our work generalizes the polaron study from transition metal oxides to van der Waals heterostructures with higher material flexibility, highlighting interlayer coupling as an extra degree of freedom to explore emergent phenomena.
View details for PubMedID 29302973
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Electronic structure of monolayer 1T'-MoTe2 grown by molecular beam epitaxy
APL MATERIALS
2018; 6 (2)
View details for DOI 10.1063/1.5004700
View details for Web of Science ID 000426999900008
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Stripe order from the perspective of the Hubbard model
npj Quantum Materials
2018; 3 (1)
View details for DOI 10.1038/s41535-018-0097-0
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Numerical evidence of fluctuating stripes in the normal state of high-Tc cuprate superconductors
SCIENCE
2017; 358 (6367): 1161-+
Abstract
Upon doping, Mott insulators often exhibit symmetry breaking where charge carriers and their spins organize into patterns known as stripes. For high-transition temperature cuprate superconductors, stripes are widely suspected to exist in a fluctuating form. We used numerically exact determinant quantum Monte Carlo calculations to demonstrate dynamical stripe correlations in the three-band Hubbard model, which represents the local electronic structure of the copper-oxygen plane. Our results, which are robust to varying parameters, cluster size, and boundary conditions, support the interpretation of experimental observations such as the hourglass magnetic dispersion and the Yamada plot of incommensurability versus doping in terms of the physics of fluctuating stripes. These findings provide a different perspective on the intertwined orders emerging from the cuprates' normal state.
View details for PubMedID 29191902
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Dynamical time-reversal symmetry breaking and photo-induced chiral spin liquids in frustrated Mott insulators
NATURE COMMUNICATIONS
2017; 8: 1192
Abstract
The search for quantum spin liquids in frustrated quantum magnets recently has enjoyed a surge of interest, with various candidate materials under intense scrutiny. However, an experimental confirmation of a gapped topological spin liquid remains an open question. Here, we show that circularly polarized light can provide a knob to drive frustrated Mott insulators into a chiral spin liquid, realizing an elusive quantum spin liquid with topological order. We find that the dynamics of a driven Kagome Mott insulator is well-captured by an effective Floquet spin model, with heating strongly suppressed, inducing a scalar spin chirality S i · (S j × S k ) term which dynamically breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the transient phase diagram and find a stable photo-induced chiral spin liquid near the equilibrium state. The results presented suggest employing dynamical symmetry breaking to engineer quantum spin liquids and access elusive phase transitions that are not readily accessible in equilibrium.
View details for PubMedID 29084937
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Decrease of d-wave pairing strength in spite of the persistence of magnetic excitations in the overdoped Hubbard model
PHYSICAL REVIEW B
2017; 96 (2)
View details for DOI 10.1103/PhysRevB.96.020503
View details for Web of Science ID 000405697700002
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Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser
SCIENCE
2017; 357 (6346): 71–74
Abstract
The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a "coherent lock-in" measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure. Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.
View details for PubMedID 28684521
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Quantum spin Hall state in monolayer 1T '-WTe2
NATURE PHYSICS
2017; 13 (7): 683-+
View details for DOI 10.1038/NPHYS4174
View details for Web of Science ID 000404629900018
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Nonequilibrium lattice-driven dynamics of stripes in nickelates using time-resolved x-ray scattering
PHYSICAL REVIEW B
2017; 95 (12)
View details for DOI 10.1103/PhysRevB.95.121105
View details for Web of Science ID 000396014600002
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Hybrid metal-organic chalcogenide nanowires with electrically conductive inorganic core through diamondoid-directed assembly.
Nature materials
2017; 16 (3): 349-355
Abstract
Controlling inorganic structure and dimensionality through structure-directing agents is a versatile approach for new materials synthesis that has been used extensively for metal-organic frameworks and coordination polymers. However, the lack of 'solid' inorganic cores requires charge transport through single-atom chains and/or organic groups, limiting their electronic properties. Here, we report that strongly interacting diamondoid structure-directing agents guide the growth of hybrid metal-organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. The strong van der Waals attraction between diamondoids overcomes steric repulsion leading to a cis configuration at the active growth front, enabling face-on addition of precursors for nanowire elongation. These nanowires have band-like electronic properties, low effective carrier masses and three orders-of-magnitude conductivity modulation by hole doping. This discovery highlights a previously unexplored regime of structure-directing agents compared with traditional surfactant, block copolymer or metal-organic framework linkers.
View details for DOI 10.1038/nmat4823
View details for PubMedID 28024157
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Modular soft x-ray spectrometer for applications in energy sciences and quantum materials.
The Review of scientific instruments
2017; 88 (1): 013110-?
Abstract
Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components. The spectrometer's optics chamber can be used with gratings operated in either inside or outside orders, and the detector assembly can be reconfigured accordingly. The spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving power when using small source (∼1μm) and detector pixels (∼5μm) with high line density gratings (∼3000 lines/mm), or high throughput at moderate resolution. We report two such spectrometers with slightly different design goals and optical parameters in this paper. We show that the spectrometer with high throughput and large energy window is particularly useful for studying the sustainable energy materials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery cathode material LiNi1/3Co1/3Mn1/3O2 can be produced in few hours using such a spectrometer. Unlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the elemental absorption edges to determine various spectral features like the localized dd excitations and non-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying such RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes hard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this modular spectrometer design can serve as the platform for further customization to meet specific scientific demands.
View details for DOI 10.1063/1.4974356
View details for PubMedID 28147697
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Distinct Electronic Structure for the Extreme Magnetoresistance in YSb
PHYSICAL REVIEW LETTERS
2016; 117 (26)
Abstract
An extreme magnetoresistance (XMR) has recently been observed in several nonmagnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.
View details for DOI 10.1103/PhysRevLett.117.267201
View details for PubMedID 28059532
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Ideal charge-density-wave order in the high-field state of superconducting YBCO
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2016; 113 (51): 14645-14650
Abstract
The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field ([Formula: see text]) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to [Formula: see text], given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an "ideal" disorder-free cuprate.
View details for DOI 10.1073/pnas.1612849113
View details for Web of Science ID 000390044900047
View details for PubMedID 27930313
View details for PubMedCentralID PMC5187671
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Nature of a single doped hole in two-leg Hubbard and t-J ladders
PHYSICAL REVIEW B
2016; 94 (15)
View details for DOI 10.1103/PhysRevB.94.155149
View details for Web of Science ID 000387016300001
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Directly Characterizing the Relative Strength and Momentum Dependence of Electron-Phonon Coupling Using Resonant Inelastic X-Ray Scattering
PHYSICAL REVIEW X
2016; 6 (4)
View details for DOI 10.1103/PhysRevX.6.041019
View details for Web of Science ID 000390219700002
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All-optical materials design of chiral edge modes in transition-metal dichalcogenides
NATURE COMMUNICATIONS
2016; 7
Abstract
Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping-instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. We develop an ab initio strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.
View details for DOI 10.1038/ncomms13074
View details for Web of Science ID 000385546900002
View details for PubMedID 27721504
View details for PubMedCentralID PMC5062430
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Time-domain pumping a quantum-critical charge density wave ordered material
PHYSICAL REVIEW B
2016; 94 (11)
View details for DOI 10.1103/PhysRevB.94.115167
View details for Web of Science ID 000385047600003
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Distinctive orbital anisotropy observed in the nematic state of a FeSe thin film
PHYSICAL REVIEW B
2016; 94 (11)
View details for DOI 10.1103/PhysRevB.94.115153
View details for Web of Science ID 000384065700002
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Superconducting Gap Anisotropy in Monolayer FeSe Thin Film
PHYSICAL REVIEW LETTERS
2016; 117 (11)
Abstract
Superconductivity originates from pairing of electrons near the Fermi energy. The Fermi surface topology and pairing symmetry are thus two pivotal characteristics of a superconductor. Superconductivity in one monolayer (1 ML) FeSe thin film has attracted great interest recently due to its intriguing interfacial properties and possibly high superconducting transition temperature over 65 K. Here, we report high-resolution measurements of the Fermi surface and superconducting gaps in 1 ML FeSe using angle-resolved photoemission spectroscopy. Two ellipselike electron pockets are clearly resolved overlapping with each other at the Brillouin zone corner. The superconducting gap is nodeless but moderately anisotropic, which puts strong constraint on determining the pairing symmetry. The gap maxima locate on the d_{xy} bands along the major axis of the ellipse and four gap minima are observed at the intersections of electron pockets. The gap maximum location combined with the Fermi surface geometry deviate from a single d-wave, extended s-wave or s_{±} gap function, suggesting an important role of the multiorbital nature of Fermi surface and orbital-dependent pairing in 1 ML FeSe. The gap minima location may be explained by a sign change on the electron pockets, or a competition between intra- and interorbital pairing.
View details for DOI 10.1103/PhysRevLett.117.117001
View details for PubMedID 27661715
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Tailoring the nature and strength of electron-phonon interactions in the SrTiO3(001) 2D electron liquid
NATURE MATERIALS
2016; 15 (8): 835-?
Abstract
Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron-phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.
View details for DOI 10.1038/NMAT4623
View details for Web of Science ID 000380849200014
View details for PubMedID 27064529
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Using RIXS to Uncover Elementary Charge and Spin Excitations
PHYSICAL REVIEW X
2016; 6 (2)
View details for DOI 10.1103/PhysRevX.6.021020
View details for Web of Science ID 000376011200002
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Characterizing the three-orbital Hubbard model with determinant quantum Monte Carlo
PHYSICAL REVIEW B
2016; 93 (15)
View details for DOI 10.1103/PhysRevB.93.155166
View details for Web of Science ID 000375202600001
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Nonequilibrium Dynamical Mean-Field Theory for the Charge-Density-Wave Phase of the Falicov-Kimball Model
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM
2016; 29 (3): 581-585
View details for DOI 10.1007/s10948-015-3304-2
View details for Web of Science ID 000371089500008
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Using Nonequilibrium Dynamics to Probe Competing Orders in a Mott-Peierls System
PHYSICAL REVIEW LETTERS
2016; 116 (8)
Abstract
Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here, we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe antiphase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which provides an approach for characterizing the underlying bosonic modes. The results from this analysis for different electronic momenta show an uneven softening due to a stronger coupling near k_{F}. This behavior reflects the strong link between the fermionic momenta, the coupling vertices, and ultimately, the bosonic susceptibilities when multiple phases compete for the ground state of the system.
View details for DOI 10.1103/PhysRevLett.116.086401
View details for Web of Science ID 000370816600003
View details for PubMedID 26967429
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Ultrafast resonant soft x-ray diffraction dynamics of the charge density wave in TbTe3
PHYSICAL REVIEW B
2016; 93 (2)
View details for DOI 10.1103/PhysRevB.93.024304
View details for Web of Science ID 000369218500004
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Raman and fluorescence characteristics of resonant inelastic X-ray scattering from doped superconducting cuprates
SCIENTIFIC REPORTS
2016; 6
Abstract
Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O(8+δ). Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast, the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors.
View details for DOI 10.1038/srep19657
View details for Web of Science ID 000368667100002
View details for PubMedCentralID PMC4726252
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Nonequilibrium response of an electron-mediated charge density wave ordered material to a large dc electric field
PHYSICAL REVIEW B
2016; 93 (4)
View details for DOI 10.1103/PhysRevB.93.045110
View details for Web of Science ID 000367894400005
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Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film.
Scientific reports
2016; 6: 32732-?
Abstract
The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.
View details for DOI 10.1038/srep32732
View details for PubMedID 27599406
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Direct observation of Higgs mode oscillations in the pump-probe photoemission spectra of electron-phonon mediated superconductors
PHYSICAL REVIEW B
2015; 92 (22)
View details for DOI 10.1103/PhysRevB.92.224517
View details for Web of Science ID 000367376200003
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Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields
SCIENCE
2015; 350 (6263): 949-952
Abstract
Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below ~150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.
View details for DOI 10.1126/science.aac6257
View details for Web of Science ID 000364955200042
View details for PubMedID 26541608
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Doping evolution of spin and charge excitations in the Hubbard model
PHYSICAL REVIEW B
2015; 92 (19)
View details for DOI 10.1103/PhysRevB.92.195108
View details for Web of Science ID 000364159300001
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Gauge invariance in the theoretical description of time-resolved angle-resolved pump/probe photoemission spectroscopy
PHYSICA SCRIPTA
2015; T165
View details for DOI 10.1088/0031-8949/2015/T165/014012
View details for Web of Science ID 000367396900014
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Magnetic excitations and phonons simultaneously studied by resonant inelastic x-ray scattering in optimally doped Bi1.5Pb0.55Sr1.6La0.4CuO6+delta
PHYSICAL REVIEW B
2015; 92 (6)
View details for DOI 10.1103/PhysRevB.92.064517
View details for Web of Science ID 000362212200011
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Origin of strong dispersion in Hubbard insulators
PHYSICAL REVIEW B
2015; 92 (7)
View details for DOI 10.1103/PhysRevB.92.075119
View details for Web of Science ID 000359344100006
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Fidelity study of superconductivity in extended Hubbard models
PHYSICAL REVIEW B
2015; 92 (2)
View details for DOI 10.1103/PhysRevB.92.024503
View details for Web of Science ID 000357635100003
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Position-Momentum Duality and Fractional Quantum Hall Effect in Chern Insulators.
Physical review letters
2015; 114 (23): 236802-?
Abstract
We develop a first quantization description of fractional Chern insulators that is the dual of the conventional fractional quantum Hall (FQH) problem, with the roles of position and momentum interchanged. In this picture, FQH states are described by anisotropic FQH liquids forming in momentum-space Landau levels in a fluctuating magnetic field. The fundamental quantum geometry of the problem emerges from the interplay of single-body and interaction metrics, both of which act as momentum-space duals of the geometrical picture of the anisotropic FQH effect. We then present a novel broad class of ideal Chern insulator lattice models that act as duals of the isotropic FQH effect. The interacting problem is well-captured by Haldane pseudopotentials and affords a detailed microscopic understanding of the interplay of interactions and nontrivial quantum geometry.
View details for PubMedID 26196819
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Position-Momentum Duality and Fractional Quantum Hall Effect in Chern Insulators
PHYSICAL REVIEW LETTERS
2015; 114 (23)
Abstract
We develop a first quantization description of fractional Chern insulators that is the dual of the conventional fractional quantum Hall (FQH) problem, with the roles of position and momentum interchanged. In this picture, FQH states are described by anisotropic FQH liquids forming in momentum-space Landau levels in a fluctuating magnetic field. The fundamental quantum geometry of the problem emerges from the interplay of single-body and interaction metrics, both of which act as momentum-space duals of the geometrical picture of the anisotropic FQH effect. We then present a novel broad class of ideal Chern insulator lattice models that act as duals of the isotropic FQH effect. The interacting problem is well-captured by Haldane pseudopotentials and affords a detailed microscopic understanding of the interplay of interactions and nontrivial quantum geometry.
View details for DOI 10.1103/PhysRevLett.114.236802
View details for Web of Science ID 000355977000010
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Direct characterization of photoinduced lattice dynamics in BaFe2As2
NATURE COMMUNICATIONS
2015; 6
Abstract
Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.
View details for DOI 10.1038/ncomms8377
View details for Web of Science ID 000357175300010
View details for PubMedID 26051704
View details for PubMedCentralID PMC4468847
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Classification of collective modes in a charge density wave by momentum-dependent modulation of the electronic band structure
PHYSICAL REVIEW B
2015; 91 (20)
View details for DOI 10.1103/PhysRevB.91.201106
View details for Web of Science ID 000354985300001
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Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene
NATURE COMMUNICATIONS
2015; 6
View details for DOI 10.1038/ncomms8047
View details for Web of Science ID 000355530700003
View details for PubMedID 25958840
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Renormalization of spectra by phase competition in the half-filled Hubbard-Holstein model
PHYSICAL REVIEW B
2015; 91 (16)
View details for DOI 10.1103/PhysRevB.91.165127
View details for Web of Science ID 000353327100007
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Fractionalization, entanglement, and separation: Understanding the collective excitations in a spin-orbital chain
PHYSICAL REVIEW B
2015; 91 (16)
View details for DOI 10.1103/PhysRevB.91.165102
View details for Web of Science ID 000352143000001
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Spin Chain in Magnetic Field: Limitations of the Large-N Mean-Field Theory
14th European Conference on Physics of Magnetism (PM)
POLISH ACAD SCIENCES INST PHYSICS. 2015: 201–3
View details for Web of Science ID 000352139600012
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Probing LaMO3 Metal and Oxygen Partial Density of States Using X-ray Emission, Absorption, and Photoelectron Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2015; 119 (4): 2063-2072
View details for DOI 10.1021/jp511931y
View details for Web of Science ID 000348753000052
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Interface ferroelectric transition near the gap-opening temperature in a single-unit-cell FeSe film grown on Nb-Doped SrTiO3 substrate.
Physical review letters
2015; 114 (3): 037002-?
Abstract
We report findings of strong anomalies in both mutual inductance and inelastic Raman spectroscopy measurements of single-unit-cell FeSe film grown on Nb-doped SrTiO3, which occur near the temperature where the superconductinglike energy gap opens. Analysis suggests that the anomaly is associated with a broadened ferroelectric transition in a thin layer near the FeSe/SrTiO3 interface. The coincidence of the ferroelectric transition and gap-opening temperatures adds credence to the central role played by the film-substrate interaction on the strong Cooper pairing in this system. We discuss scenarios that could explain such a coincidence.
View details for PubMedID 25659015
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Interface Ferroelectric Transition near the Gap-Opening Temperature in a Single-Unit-Cell FeSe Film Grown on Nb-Doped SrTiO_{3} Substrate.
Physical review letters
2015; 114 (3): 037002-?
Abstract
We report findings of strong anomalies in both mutual inductance and inelastic Raman spectroscopy measurements of single-unit-cell FeSe film grown on Nb-doped SrTiO3, which occur near the temperature where the superconductinglike energy gap opens. Analysis suggests that the anomaly is associated with a broadened ferroelectric transition in a thin layer near the FeSe/SrTiO3 interface. The coincidence of the ferroelectric transition and gap-opening temperatures adds credence to the central role played by the film-substrate interaction on the strong Cooper pairing in this system. We discuss scenarios that could explain such a coincidence.
View details for PubMedID 25659015
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Direct spectroscopic evidence for phase competition between the pseudogap and superconductivity in Bi2Sr2CaCu2O8+delta
NATURE MATERIALS
2015; 14 (1): 37-42
Abstract
In the high-temperature (Tc) cuprate superconductors, a growing body of evidence suggests that the pseudogap phase, existing below the pseudogap temperature T(∗), is characterized by some broken electronic symmetries distinct from those associated with superconductivity. In particular, recent scattering experiments have suggested that charge ordering competes with superconductivity. However, no direct link of an interplay between the two phases has been identified from the important low-energy excitations. Here, we report an antagonistic singularity at Tc in the spectral weight of Bi2Sr2CaCu2O8+δ as compelling evidence for phase competition, which persists up to a high hole concentration p ~ 0.22. Comparison with theoretical calculations confirms that the singularity is a signature of competition between the order parameters for the pseudogap and superconductivity. The observation of the spectroscopic singularity at finite temperatures over a wide doping range provides new insights into the nature of the competitive interplay between the two orders and the complex phase diagram near the pseudogap critical point.
View details for DOI 10.1038/NMAT4116
View details for Web of Science ID 000346430100011
View details for PubMedID 25362356
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Why LiFePO4 is a safe battery electrode: Coulomb repulsion induced electron-state reshuffling upon lithiation
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2015; 17 (39): 26369-26377
Abstract
LiFePO4 is a battery cathode material with high safety standards due to its unique electronic structure. We performed systematic experimental and theoretical studies based on soft X-ray emission, absorption, and hard X-ray Raman spectroscopy of LixFePO4 nanoparticles and single crystals. The results clearly show a non-rigid electron-state reconfiguration of both the occupied and unoccupied Fe-3d and O-2p states during the (de)lithiation process. We focus on the energy configurations of the occupied states of LiFePO4 and the unoccupied states of FePO4, which are the critical states where electrons are removed and injected during the charge and discharge process, respectively. In LiFePO4, the soft X-ray emission spectroscopy shows that, due to the Coulomb repulsion effect, the occupied Fe-3d states with the minority spin sit close to the Fermi level. In FePO4, the soft X-ray absorption and hard X-ray Raman spectroscopy show that the unoccupied Fe-3d states again sit close to the Fermi level. These critical 3d electron state configurations are consistent with the calculations based on modified Becke and Johnson potentials GGA+U (MBJGGA+U) framework, which improves the overall lineshape prediction compared with the conventionally used GGA+U method. The combined experimental and theoretical studies show that the non-rigid electron state reshuffling guarantees the stability of oxygen during the redox reaction throughout the charge and discharge process of LiFePO4 electrodes, leading to the intrinsic safe performance of the electrodes.
View details for DOI 10.1039/c5cp04739k
View details for Web of Science ID 000362291300078
View details for PubMedID 26388021
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Theory of Floquet band formation and local pseudospin textures in pump-probe photoemission of graphene.
Nature communications
2015; 6: 7047-?
Abstract
Ultrafast materials science promises optical control of physical properties of solids. Continuous-wave circularly polarized laser driving was predicted to induce a light-matter coupled state with an energy gap and a quantum Hall effect, coined Floquet topological insulator. Whereas the envisioned Floquet topological insulator requires high-frequency pumping to obtain well-separated Floquet bands, a follow-up question regards the creation of Floquet-like states in graphene with realistic low-frequency laser pulses. Here we predict that short optical pulses attainable in experiments can lead to local spectral gaps and novel pseudospin textures in graphene. Pump-probe photoemission spectroscopy can track these states by measuring sizeable energy gaps and Floquet band formation on femtosecond time scales. Analysing band crossings and pseudospin textures near the Dirac points, we identify new states with optically induced nontrivial changes of sublattice mixing that leads to Berry curvature corrections of electrical transport and magnetization.
View details for DOI 10.1038/ncomms8047
View details for PubMedID 25958840
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Direct characterization of photoinduced lattice dynamics in BaFe2As2.
Nature communications
2015; 6: 7377-?
Abstract
Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.
View details for DOI 10.1038/ncomms8377
View details for PubMedID 26051704
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Balancing Act: Evidence for a Strong Subdominant d-Wave Pairing Channel in Ba0.6K0.4Fe2As2
PHYSICAL REVIEW X
2014; 4 (4)
View details for DOI 10.1103/PhysRevX.4.041046
View details for Web of Science ID 000349072800001
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Numerical exploration of spontaneous broken symmetries in multiorbital Hubbard models
PHYSICAL REVIEW B
2014; 90 (22)
View details for DOI 10.1103/PhysRevB.90.224507
View details for Web of Science ID 000346607200008
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Interfacial mode coupling as the origin of the enhancement of T-c in FeSe films on SrTiO3
NATURE
2014; 515 (7526): 245-U207
Abstract
Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3 or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 kelvin), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3 (refs 5, 6, 7), which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3.
View details for DOI 10.1038/nature13894
View details for PubMedID 25391962
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Beyond Planck-Einstein quanta: Amplitude-driven quantum excitation
PHYSICAL REVIEW B
2014; 90 (19)
View details for DOI 10.1103/PhysRevB.90.195104
View details for Web of Science ID 000344487900002
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Asymmetry of collective excitations in electron- and hole-doped cuprate superconductors
NATURE PHYSICS
2014; 10 (11): 883-889
View details for DOI 10.1038/NPHYS3117
View details for Web of Science ID 000344846700024
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Distinguishing Bulk and Surface Electron-Phonon Coupling in the Topological Insulator Bi2Se3 Using Time-Resolved Photoemission Spectroscopy
PHYSICAL REVIEW LETTERS
2014; 113 (15)
Abstract
We report time- and angle-resolved photoemission spectroscopy measurements on the topological insulator Bi(2)Se(3). We observe oscillatory modulations of the electronic structure of both the bulk and surface states at a frequency of 2.23 THz due to coherent excitation of an A(1g) phonon mode. A distinct, additional frequency of 2.05 THz is observed in the surface state only. The lower phonon frequency at the surface is attributed to the termination of the crystal and thus reduction of interlayer van der Waals forces, which serve as restorative forces for out-of-plane lattice distortions. Density functional theory calculations quantitatively reproduce the magnitude of the surface phonon softening. These results represent the first band-resolved evidence of the A(1g) phonon mode coupling to the surface state in a topological insulator.
View details for DOI 10.1103/PhysRevLett.113.157401
View details for Web of Science ID 000344052200011
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Exact solution for high harmonic generation and the response to an ac driving field for a charge density wave insulator
PHYSICAL REVIEW B
2014; 90 (11)
View details for DOI 10.1103/PhysRevB.90.115113
View details for Web of Science ID 000341259600002
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Effect of dynamical spectral weight redistribution on effective interactions in time-resolved spectroscopy
PHYSICAL REVIEW B
2014; 90 (7)
View details for DOI 10.1103/PhysRevB.90.075126
View details for Web of Science ID 000341256600003
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Ultrafast electron dynamics in the topological insulator Bi2Se3 studied by time-resolved photoemission spectroscopy
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
2014; 195: 249-257
View details for DOI 10.1016/j.elspec.2014.01.005
View details for Web of Science ID 000342872800036
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Energy gaps in high-transition-temperature cuprate superconductors
NATURE PHYSICS
2014; 10 (7): 483-495
View details for DOI 10.1038/NPHYS3009
View details for Web of Science ID 000338843100014
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Direct observation of bulk charge modulations in optimally doped Bi1.5Pb0.6Sr1.54CaCu2O8+delta
PHYSICAL REVIEW B
2014; 89 (22)
View details for DOI 10.1103/PhysRevB.89.220511
View details for Web of Science ID 000339049000001
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Exact solution for Bloch oscillations of a simple charge-density-wave insulator
PHYSICAL REVIEW B
2014; 89 (23)
View details for DOI 10.1103/PhysRevB.89.235129
View details for Web of Science ID 000338640100003
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Bandgap closure and reopening in CsAuI3 at high pressure
PHYSICAL REVIEW B
2014; 89 (24)
View details for DOI 10.1103/PhysRevB.89.245109
View details for Web of Science ID 000336976400003
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Angle-resolved photoemission spectroscopy study of HgBa2CuO4+delta
PHYSICAL REVIEW B
2014; 89 (19)
View details for DOI 10.1103/PhysRevB.89.195141
View details for Web of Science ID 000336841000003
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Nonequilibrium "Melting" of a Charge Density Wave Insulator via an Ultrafast Laser Pulse.
Physical review letters
2014; 112 (17): 176404-?
Abstract
We employ an exact solution of the simplest model for pump-probe time-resolved photoemission spectroscopy in charge-density-wave systems to show how, in nonequilibrium, the gap in the density of states disappears while the charge density remains modulated, and then the gap reforms after the pulse has passed. This nonequilibrium scenario qualitatively describes the common short-time experimental features in TaS_{2} and TbTe_{3}, indicating a quasiuniversality for nonequilibrium "melting" with qualitative features that can be easily understood within a simple picture.
View details for PubMedID 24836262
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Real-space visualization of remnant mott gap and magnon excitations.
Physical review letters
2014; 112 (15): 156402-?
Abstract
We demonstrate the ability to visualize real-space dynamics of charge gap and magnon excitations in the Mott phase of the single-band Hubbard model and the remnants of these excitations with hole or electron doping. At short times, the character of magnetic and charge excitations is maintained even for large doping away from the Mott and antiferromagnetic phases. Doping influences both the real-space patterns and long timescales of these excitations with a clear carrier asymmetry attributable to particle-hole symmetry breaking in the underlying model. Further, a rapidly oscillating charge-density-wave-like pattern weakens, but persists as a visible demonstration of a subleading instability at half-filling which remains upon doping. The results offer an approach to analyzing the behavior of systems where momentum space is either inaccessible or poorly defined.
View details for PubMedID 24785060
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Dynamic competition between spin-density wave order and superconductivity in underdoped Ba1-xKxFe2As2
NATURE COMMUNICATIONS
2014; 5
View details for DOI 10.1038/ncomms4711
View details for Web of Science ID 000335223100002
View details for PubMedID 24762657
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Charge-orbital-lattice coupling effects in the dd excitation profile of one-dimensional cuprates
PHYSICAL REVIEW B
2014; 89 (4)
View details for DOI 10.1103/PhysRevB.89.041104
View details for Web of Science ID 000332204000001
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Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering.
Nature communications
2014; 5: 3314-?
Abstract
How coherent quasiparticles emerge by doping quantum antiferromagnets is a key question in correlated electron systems, whose resolution is needed to elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray scattering (RIXS) experiments in hole-doped cuprates have purported to measure high-energy collective spin excitations that persist well into the overdoped regime and bear a striking resemblance to those found in the parent compound, challenging the perception that spin excitations should weaken with doping and have a diminishing effect on superconductivity. Here we show that RIXS at the Cu L3-edge indeed provides access to the spin dynamical structure factor once one considers the full influence of light polarization. Further we demonstrate that high-energy spin excitations do not correlate with the doping dependence of Tc, while low-energy excitations depend sensitively on doping and show ferromagnetic correlations. This suggests that high-energy spin excitations are marginal to pairing in cuprate superconductors.
View details for DOI 10.1038/ncomms4314
View details for PubMedID 24577074
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Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering.
Nature communications
2014; 5: 3314-?
View details for DOI 10.1038/ncomms4314
View details for PubMedID 24577074
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Dynamic competition between spin-density wave order and superconductivity in underdoped Ba(1-x)K(x)Fe2As2.
Nature communications
2014; 5: 3711-?
Abstract
An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba(1-x)K(x)Fe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials.
View details for DOI 10.1038/ncomms4711
View details for PubMedID 24762657
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Examining Electron-Boson Coupling Using Time-Resolved Spectroscopy
PHYSICAL REVIEW X
2013; 3 (4)
View details for DOI 10.1103/PhysRevX.3.041033
View details for Web of Science ID 000330128900001
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Tunneling spectroscopy for probing orbital anisotropy in iron pnictides
PHYSICAL REVIEW B
2013; 88 (17)
View details for DOI 10.1103/PhysRevB.88.174518
View details for Web of Science ID 000327933500007
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Existence of Orbital Order and its Fluctuation in Superconducting Ba(Fe1-xCox)(2)As-2 Single Crystals Revealed by X-ray Absorption Spectroscopy
PHYSICAL REVIEW LETTERS
2013; 111 (21)
Abstract
We performed temperature dependent x-ray linear dichroism (XLD) experiments on an iron pnictide system, Ba(Fe(1-x)Co(x))2As2 with x=0.00, 0.05, 0.08, and 0.10 to experimentally verify the existence of orbital ordering (OO). Substantial XLD was observed in polarization dependent x-ray absorption spectra of Fe L edges. By exploiting the difference in the temperature dependent behaviors, OO, and structure contributions to XLD could be clearly separated. The observed OO signal indicates different occupation numbers for d(yz) and d(zx) orbitals and supports the existence of ferro-OO. The results are also consistent with the theoretical prediction. Moreover, we find substantial OO signal well above the structural and magnetic transition temperatures, which suggests the existence of strong OO fluctuations up to high temperatures.
View details for DOI 10.1103/PhysRevLett.111.217001
View details for Web of Science ID 000327245600025
View details for PubMedID 24313517
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Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2Se3
PHYSICAL REVIEW LETTERS
2013; 111 (13)
Abstract
We characterize the occupied and unoccupied electronic structure of the topological insulator Bi2Se3 by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.
View details for DOI 10.1103/PhysRevLett.111.136802
View details for PubMedID 24116801
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Time-dependent charge-order and spin-order recovery in striped systems
PHYSICAL REVIEW B
2013; 88 (12)
View details for DOI 10.1103/PhysRevB.88.125114
View details for Web of Science ID 000324231000003
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Electron-mediated relaxation following ultrafast pumping of strongly correlated materials: model evidence of a correlation-tuned crossover between thermal and nonthermal states.
Physical review letters
2013; 111 (7): 077401-?
Abstract
We examine electron-electron mediated relaxation following ultrafast electric field pump excitation of the fermionic degrees of freedom in the Falicov-Kimball model for correlated electrons. The results reveal a dichotomy in the temporal evolution of the system as one tunes through the Mott metal-to-insulator transition: in the metallic regime relaxation can be characterized by evolution toward a steady state well described by Fermi-Dirac statistics with an increased effective temperature; however, in the insulating regime this quasithermal paradigm breaks down with relaxation toward a nonthermal state with a complicated electronic distribution as a function of momentum. We characterize the behavior by studying changes in the energy, photoemission response, and electronic distribution as functions of time. This relaxation may be observable qualitatively on short enough time scales that the electrons behave like an isolated system not in contact with additional degrees of freedom which would act as a thermal bath, especially when using strong driving fields and studying materials whose physics may manifest the effects of correlations.
View details for PubMedID 23992080
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Electron-Mediated Relaxation Following Ultrafast Pumping of Strongly Correlated Materials: Model Evidence of a Correlation-Tuned Crossover between Thermal and Nonthermal States
PHYSICAL REVIEW LETTERS
2013; 111 (7)
View details for DOI 10.1103/PhysRevLett.111.077401
View details for Web of Science ID 000323036500004
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Mapping of unoccupied states and relevant bosonic modes via the time-dependent momentum distribution
PHYSICAL REVIEW B
2013; 87 (23)
View details for DOI 10.1103/PhysRevB.87.235139
View details for Web of Science ID 000321061000001
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Role of Lattice Coupling in Establishing Electronic and Magnetic Properties in Quasi-One-Dimensional Cuprates
PHYSICAL REVIEW LETTERS
2013; 110 (26)
Abstract
High resolution resonant inelastic x-ray scattering has been performed to reveal the role of lattice coupling in a family of quasi-1D insulating cuprates, Ca2+5xY2-5xCu5O10. Site-dependent low-energy excitations arising from progressive emissions of a 70 meV lattice vibrational mode are resolved for the first time, providing a direct measurement of electron-lattice coupling strength. We show that such electron-lattice coupling causes doping-dependent distortions of the Cu-O-Cu bond angle, which sets the intrachain spin exchange interactions. Our results indicate that the lattice degrees of freedom are fully integrated into the electronic behavior in low-dimensional systems.
View details for DOI 10.1103/PhysRevLett.110.265502
View details for Web of Science ID 000320960300012
View details for PubMedID 23848894
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Determinant quantum Monte Carlo study of the two-dimensional single-band Hubbard-Holstein model
PHYSICAL REVIEW B
2013; 87 (23)
View details for DOI 10.1103/PhysRevB.87.235133
View details for Web of Science ID 000320949600005
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Doping evolution of the oxygen K-edge x-ray absorption spectra of cuprate superconductors using a three-orbital Hubbard model
PHYSICAL REVIEW B
2013; 87 (16)
View details for DOI 10.1103/PhysRevB.87.165144
View details for Web of Science ID 000318520900008
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Real-Time Manifestation of Strongly Coupled Spin and Charge Order Parameters in Stripe-Ordered La_{1.75}Sr_{0.25}NiO_{4} Nickelate Crystals Using Time-Resolved Resonant X-Ray Diffraction.
Physical review letters
2013; 110 (12): 127404-?
Abstract
We investigate the order parameter dynamics of the stripe-ordered nickelate, La_{1.75}Sr_{0.25}NiO_{4}, using time-resolved resonant x-ray diffraction. In spite of distinct spin and charge energy scales, the two order parameters' amplitude dynamics are found to be linked together due to strong coupling. Additionally, the vector nature of the spin sector introduces a longer reorientation time scale which is absent in the charge sector. These findings demonstrate that the correlation linking the symmetry-broken states does not unbind during the nonequilibrium process, and the time scales are not necessarily associated with the characteristic energy scales of individual degrees of freedom.
View details for PubMedID 25166848
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Real-Time Manifestation of Strongly Coupled Spin and Charge Order Parameters in Stripe-Ordered La1.75Sr0.25NiO4 Nickelate Crystals Using Time-Resolved Resonant X-Ray Diffraction
PHYSICAL REVIEW LETTERS
2013; 110 (12)
Abstract
We investigate the order parameter dynamics of the stripe-ordered nickelate, La_{1.75}Sr_{0.25}NiO_{4}, using time-resolved resonant x-ray diffraction. In spite of distinct spin and charge energy scales, the two order parameters' amplitude dynamics are found to be linked together due to strong coupling. Additionally, the vector nature of the spin sector introduces a longer reorientation time scale which is absent in the charge sector. These findings demonstrate that the correlation linking the symmetry-broken states does not unbind during the nonequilibrium process, and the time scales are not necessarily associated with the characteristic energy scales of individual degrees of freedom.
View details for DOI 10.1103/PhysRevLett.110.127404
View details for Web of Science ID 000316411100019
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Hot electron transport in a strongly correlated transition-metal oxide
SCIENTIFIC REPORTS
2013; 3
Abstract
Oxide heterointerfaces are ideal for investigating strong correlation effects to electron transport, relevant for oxide-electronics. Using hot-electrons, we probe electron transport perpendicular to the La₀.₇Sr₀.₃MnO₃ (LSMO)- Nb-doped SrTiO₃ (Nb:STO) interface and find the characteristic hot-electron attenuation length in LSMO to be 1.48 ± 0.10 unit cells (u.c.) at -1.9 V, increasing to 2.02 ± 0.16 u.c. at -1.3 V at room temperature. Theoretical analysis of this energy dispersion reveals the dominance of electron-electron and polaron scattering. Direct visualization of the local electron transport shows different transmission at the terraces and at the step-edges.
View details for DOI 10.1038/srep01274
View details for Web of Science ID 000314864800002
View details for PubMedID 23429420
View details for PubMedCentralID PMC3572443
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Theoretical description of high-order harmonic generation in solids
NEW JOURNAL OF PHYSICS
2013; 15
View details for DOI 10.1088/1367-2630/15/2/023003
View details for Web of Science ID 000314516500003
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Measurement of Coherent Polarons in the Strongly Coupled Antiferromagnetically Ordered Iron-Chalcogenide Fe1.02Te using Angle-Resolved Photoemission Spectroscopy
PHYSICAL REVIEW LETTERS
2013; 110 (3)
Abstract
The nature of metallicity and the level of electronic correlations in the antiferromagnetically ordered parent compounds are two important open issues for the iron-based superconductivity. We perform a temperature-dependent angle-resolved photoemission spectroscopy study of Fe(1.02)Te, the parent compound for iron chalcogenide superconductors. Deep in the antiferromagnetic state, the spectra exhibit a "peak-dip-hump" line shape associated with two clearly separate branches of dispersion, characteristics of polarons seen in manganites and lightly doped cuprates. As temperature increases towards the Néel temperature (T(N)), we observe a decreasing renormalization of the peak dispersion and a counterintuitive sharpening of the hump linewidth, suggestive of an intimate connection between the weakening electron-phonon (e-ph) coupling and antiferromagnetism. Our finding points to the highly correlated nature of the Fe(1.02)Te ground state featured by strong interactions among the charge, spin, and lattice and a good metallicity plausibly contributed by the coherent polaron motion.
View details for DOI 10.1103/PhysRevLett.110.037003
View details for Web of Science ID 000313755000014
View details for PubMedID 23373946
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Alternative route to charge density wave formation in multiband systems
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2013; 110 (1): 64-69
Abstract
Charge and spin density waves, periodic modulations of the electron, and magnetization densities, respectively, are among the most abundant and nontrivial low-temperature ordered phases in condensed matter. The ordering direction is widely believed to result from the Fermi surface topology. However, several recent studies indicate that this common view needs to be supplemented. Here, we show how an enhanced electron-lattice interaction can contribute to or even determine the selection of the ordering vector in the model charge density wave system ErTe(3). Our joint experimental and theoretical study allows us to establish a relation between the selection rules of the electronic light scattering spectra and the enhanced electron-phonon coupling in the vicinity of band degeneracy points. This alternative proposal for charge density wave formation may be of general relevance for driving phase transitions into other broken-symmetry ground states, particularly in multiband systems, such as the iron-based superconductors.
View details for DOI 10.1073/pnas.1214745110
View details for Web of Science ID 000313630300027
View details for PubMedID 23248317
View details for PubMedCentralID PMC3538267
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Competition Between Antiferromagnetic and Charge-Density-Wave Order in the Half-Filled Hubbard-Holstein Model
PHYSICAL REVIEW LETTERS
2012; 109 (24)
Abstract
We present a determinant quantum Monte Carlo study of the competition between instantaneous on-site Coulomb repulsion and retarded phonon-mediated attraction between electrons, as described by the two-dimensional Hubbard-Holstein model. At half filling, we find a strong competition between antiferromagnetism (AFM) and charge-density-wave (CDW) order. We demonstrate that a simple picture of AFM-CDW competition that incorporates the phonon-mediated attraction into an effective-U Hubbard model requires significant refinement. Specifically, retardation effects slow the onset of charge order so that CDW order remains absent even when the effective U is negative. This delay opens a window where neither AFM nor CDW order is well established and where there are signatures of a possible metallic phase.
View details for DOI 10.1103/PhysRevLett.109.246404
View details for Web of Science ID 000312068300027
View details for PubMedID 23368352
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Uncovering selective excitations using the resonant profile of indirect inelastic x-ray scattering in correlated materials: observing two-magnon scattering and relation to the dynamical structure factor
NEW JOURNAL OF PHYSICS
2012; 14
View details for DOI 10.1088/1367-2630/14/11/113038
View details for Web of Science ID 000311580900003
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X-ray Emission Spectroscopy of Cerium Across the gamma-alpha Volume Collapse Transition
PHYSICAL REVIEW LETTERS
2012; 109 (19)
Abstract
High-pressure x-ray emission measurements are used to provide crucial evidence in the longstanding debate over the nature of the isostructural (α, γ) volume collapse in elemental cerium. Extended local atomic model calculations show that the satellite of the Lγ emission line offers direct access to the total angular momentum observable (J(2)). This satellite experiences a 30% steplike decrease across the volume collapse, validating the Kondo model in conjunction with previous measurements. Direct comparisons are made with previous predictions by dynamical mean field theory. A general experimental methodology is demonstrated for analogous work on a wide range of strongly correlated f-electron systems.
View details for DOI 10.1103/PhysRevLett.109.195705
View details for Web of Science ID 000310869600010
View details for PubMedID 23215404
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Phase competition in trisected superconducting dome
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2012; 109 (45): 18332-18337
Abstract
A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi(2)Sr(2)CaCu(2)O(8+δ), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T(c) and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
View details for DOI 10.1073/pnas.1209471109
View details for Web of Science ID 000311156700031
View details for PubMedID 23093670
View details for PubMedCentralID PMC3494935
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Pulsed high harmonic generation of light due to pumped Bloch oscillations in noninteracting metals
PHYSICA SCRIPTA
2012; T151
View details for DOI 10.1088/0031-8949/2012/T151/014062
View details for Web of Science ID 000311961700063
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Quantum Dynamics of the Hubbard-Holstein Model in Equilibrium and Nonequilibrium: Application to Pump-Probe Phenomena
PHYSICAL REVIEW LETTERS
2012; 109 (17)
Abstract
The spectral response and physical features of the 2D Hubbard-Holstein model are calculated both in equilibrium at zero and low chemical dopings, and after an ultrashort powerful light pulse, in undoped systems. At equilibrium and at strong charge-lattice couplings, the optical conductivity reveals a three-peak structure in agreement with experimental observations. After an ultrashort pulse and at nonzero electron-phonon interaction, phonon and spin subsystems oscillate with the phonon period T(ph)≈80 fs. The decay time of the phonon oscillations is about 150-200 fs, similar to the relaxation time of the charge system. We propose a criterion for observing these oscillations in high T(c) compounds: the time span of the pump light pulse τ(pump) has to be shorter than the phonon oscillation period T(ph).
View details for DOI 10.1103/PhysRevLett.109.176402
View details for Web of Science ID 000310200100023
View details for PubMedID 23215207
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Quasiparticle interference and the interplay between superconductivity and density wave order in the cuprates
PHYSICAL REVIEW B
2012; 86 (13)
View details for DOI 10.1103/PhysRevB.86.134509
View details for Web of Science ID 000309577400005
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Superconductivity distorted by the coexisting pseudogap in the antinodal region of Bi1.5Pb0.55Sr1.6La0.4CuO6+delta: A photon-energy-dependent angle-resolved photoemission study
PHYSICAL REVIEW B
2012; 86 (9)
View details for DOI 10.1103/PhysRevB.86.094504
View details for Web of Science ID 000308287300015
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Phase fluctuations and the absence of topological defects in a photo-excited charge-ordered nickelate
NATURE COMMUNICATIONS
2012; 3
Abstract
The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La(1.75)Sr(0.25)NiO(4) to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter.
View details for DOI 10.1038/ncomms1837
View details for Web of Science ID 000304611400033
View details for PubMedID 22588300
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Resonant enhancement of charge density wave diffraction in the rare-earth tritellurides
PHYSICAL REVIEW B
2012; 85 (15)
View details for DOI 10.1103/PhysRevB.85.155142
View details for Web of Science ID 000303309600003
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Evidence for the Importance of Extended Coulomb Interactions and Forward Scattering in Cuprate Superconductors
PHYSICAL REVIEW LETTERS
2012; 108 (16)
Abstract
The prevalent view of the high-temperature superconducting cuprates is that their essential low-energy physics is captured by local Coulomb interactions. However, this view been challenged recently by studies indicating the importance of longer-range components. Motivated by this, we demonstrate the importance of these components by examining the electron-phonon (e-ph) interaction with acoustic phonons in connection with the recently discovered renormalization in the near-nodal low-energy (~8-15 meV) dispersion of Bi(2)Sr(2)CaCu(2)O(8+δ). By studying its nontrivial momentum and doping dependence we conclude a predominance of forward scattering arising from the direct interplay between the e-ph and extended Coulomb interactions. Our results thus demonstrate how the low-energy renormalization can provide a pathway to new insights into how these interactions interplay with one another and influence pairing and dynamics in the cuprates.
View details for DOI 10.1103/PhysRevLett.108.166404
View details for Web of Science ID 000303070600015
View details for PubMedID 22680740
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Phase transitions in spin-orbital models with spin-space anisotropies for iron pnictides: Monte Carlo simulations
PHYSICAL REVIEW B
2012; 85 (5)
View details for DOI 10.1103/PhysRevB.85.054411
View details for Web of Science ID 000300084800003
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Investigation of particle-hole asymmetry in the cuprates via electronic Raman scattering
PHYSICAL REVIEW B
2011; 84 (23)
View details for DOI 10.1103/PhysRevB.84.235114
View details for Web of Science ID 000297765200006
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Coincidence between energy gaps and Kohn anomalies in conventional superconductors
PHYSICAL REVIEW B
2011; 84 (17)
View details for DOI 10.1103/PhysRevB.84.174523
View details for Web of Science ID 000297294600010
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Fidelity study of the superconducting phase diagram in the two-dimensional single-band Hubbard model
PHYSICAL REVIEW B
2011; 84 (12)
View details for DOI 10.1103/PhysRevB.84.125113
View details for Web of Science ID 000294777400007
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Polaronic metal in lightly doped high-T-c cuprates
EPL
2011; 95 (5)
View details for DOI 10.1209/0295-5075/95/57007
View details for Web of Science ID 000294325500031
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Probing high-energy electronic excitations in NiO using inelastic neutron scattering
PHYSICAL REVIEW B
2011; 84 (8)
View details for DOI 10.1103/PhysRevB.84.085132
View details for Web of Science ID 000294326200004
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Resonant inelastic x-ray scattering studies of elementary excitations
REVIEWS OF MODERN PHYSICS
2011; 83 (2)
View details for DOI 10.1103/RevModPhys.83.705
View details for Web of Science ID 000292042300001
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Anisotropic quasiparticle lifetimes in Fe-based superconductors
PHYSICAL REVIEW B
2011; 83 (18)
View details for DOI 10.1103/PhysRevB.83.184516
View details for Web of Science ID 000290864400005
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High-energy anomaly in Nd2-xCexCuO4 investigated by angle-resolved photoemission spectroscopy and quantum Monte Carlo simulations
PHYSICAL REVIEW B
2011; 83 (19)
View details for DOI 10.1103/PhysRevB.83.195123
View details for Web of Science ID 000290711300003
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Symmetry-breaking orbital anisotropy observed for detwinned Ba(Fe1-xCox)(2)As-2 above the spin density wave transition
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (17): 6878-6883
View details for DOI 10.1073/pnas.1015572108
View details for Web of Science ID 000289888500040
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Reaffirming the d(x2-y2) Superconducting Gap Using the Autocorrelation Angle-Resolved Photoemission Spectroscopy of Bi1.5Pb0.55Sr1.6La0.4CuO6+delta
PHYSICAL REVIEW LETTERS
2011; 106 (16)
Abstract
Knowledge of the gap function is important to understand the pairing mechanism for high-temperature (T(c)) superconductivity. However, Fourier transform scanning tunneling spectroscopy (FT STS) and angle-resolved photoemission spectroscopy (ARPES) in the cuprates have reported contradictory gap functions, with FT-STS results deviating strongly from a canonical d(x2-y2) form. By applying an "octet model" analysis to autocorrelation ARPES, we reveal that a contradiction occurs because the octet model does not consider the effects of matrix elements and the pseudogap. This reaffirms the canonical d(x2-y2) superconducting gap around the node, which can be directly determined from ARPES. Further, our study suggests that the FT-STS reported fluctuating superconductivity around the node at far above T(c) is not necessary to explain the existence of the quasiparticle interference at low energy.
View details for DOI 10.1103/PhysRevLett.106.167003
View details for Web of Science ID 000290097500013
View details for PubMedID 21599403
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Revealing the degree of magnetic frustration by non-magnetic impurities
NEW JOURNAL OF PHYSICS
2011; 13
View details for DOI 10.1088/1367-2630/13/4/043025
View details for Web of Science ID 000289994100002
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From a Single-Band Metal to a High-Temperature Superconductor via Two Thermal Phase Transitions
SCIENCE
2011; 331 (6024): 1579-1583
Abstract
The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T(c)), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.
View details for DOI 10.1126/science.1198415
View details for PubMedID 21436447
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Theory of Two-Magnon Raman Scattering in Iron Pnictides and Chalcogenides
PHYSICAL REVIEW LETTERS
2011; 106 (6)
Abstract
Although the parent iron-based pnictides and chalcogenides are itinerant antiferromagnets, the use of local moment picture to understand their magnetic properties is still widespread. We study magnetic Raman scattering from a local moment perspective for various quantum spin models proposed for this new class of superconductors. These models vary greatly in the level of magnetic frustration and show a vastly different two-magnon Raman response. Light scattering by two-magnon excitations thus provides a robust and independent measure of the underlying spin interactions. In accord with other recent experiments, our results indicate that the amount of magnetic frustration in these systems may be small.
View details for DOI 10.1103/PhysRevLett.106.067002
View details for Web of Science ID 000287196900011
View details for PubMedID 21405486
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Numerical studies of photon-based spectroscopies on high-T-c superconductors
COMPUTER PHYSICS COMMUNICATIONS
2011; 182 (1): 106-108
View details for DOI 10.1016/j.cpc.2010.08.017
View details for Web of Science ID 000285119900034
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Polaronic metal in lightly doped high-Tc cuprates
Europhys. Lett.
2011; 95 (5)
View details for DOI 10.1209/0295-5075/95/57007
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Temporal response of nonequilibrium correlated electrons
COMPUTER PHYSICS COMMUNICATIONS
2011; 182 (1): 109-111
View details for DOI 10.1016/j.cpc.2010.05.020
View details for Web of Science ID 000285119900035
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Pinpointing gap minima in Ba(Fe0.94Co0.06)(2)As-2 via band-structure calculations and electronic Raman scattering
PHYSICAL REVIEW B
2010; 82 (18)
View details for DOI 10.1103/PhysRevB.82.180502
View details for Web of Science ID 000283647300002
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ARPES studies of cuprate Fermiology: superconductivity, pseudogap and quasiparticle dynamics
NEW JOURNAL OF PHYSICS
2010; 12
View details for DOI 10.1088/1367-2630/12/10/105008
View details for Web of Science ID 000284770500004
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High-pressure evolution of Fe2O3 electronic structure revealed by x-ray absorption
PHYSICAL REVIEW B
2010; 82 (14)
View details for DOI 10.1103/PhysRevB.82.144428
View details for Web of Science ID 000283117100008
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Unraveling the Nature of Charge Excitations in La2CuO4 with Momentum-Resolved Cu K-Edge Resonant Inelastic X-Ray Scattering
PHYSICAL REVIEW LETTERS
2010; 105 (17)
Abstract
The results of model calculations using exact diagonalization reveal the orbital character of states associated with different Raman loss peaks in Cu K-edge resonant inelastic x-ray scattering (RIXS) from La₂CuO₄. The model includes electronic orbitals necessary to highlight the nonlocal Zhang-Rice singlet, charge transfer, and d-d excitations, as well as states with apical oxygen 2p(z) character. The dispersion of these excitations is discussed with prospects for resonant final state wave-function mapping. A good agreement with experiments emphasizes the substantial multiorbital character of RIXS profiles in the energy transfer range 1-6 eV.
View details for DOI 10.1103/PhysRevLett.105.177401
View details for Web of Science ID 000283054700017
View details for PubMedID 21231077
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Effect of disorder on the electronic Raman scattering in the superconducting state of iron pnictides
PHYSICAL REVIEW B
2010; 82 (13)
View details for DOI 10.1103/PhysRevB.82.134506
View details for Web of Science ID 000282506700014
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Orbital order and spontaneous orthorhombicity in iron pnictides
PHYSICAL REVIEW B
2010; 82 (10)
View details for DOI 10.1103/PhysRevB.82.100504
View details for Web of Science ID 000281845400002
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Systematic study of electron-phonon coupling to oxygen modes across the cuprates
PHYSICAL REVIEW B
2010; 82 (6)
View details for DOI 10.1103/PhysRevB.82.064513
View details for Web of Science ID 000281016800003
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Insights on the cuprate high energy anomaly observed in ARPES
International Workshop on Strong Correlations and Angle-Resolved Photoemission Spectroscopy
ELSEVIER SCIENCE BV. 2010: 31–34
View details for DOI 10.1016/j.elspec.2010.06.001
View details for Web of Science ID 000281084100008
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Density of states modulations from oxygen phonons in d-wave superconductors: Reconciling angle-resolved photoemission spectroscopy and scanning tunneling microscopy
PHYSICAL REVIEW B
2010; 81 (21)
View details for DOI 10.1103/PhysRevB.81.214512
View details for Web of Science ID 000278654300001
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Particle-hole symmetry breaking in the pseudogap state of Bi2201
NATURE PHYSICS
2010; 6 (6): 414-418
View details for DOI 10.1038/NPHYS1632
View details for Web of Science ID 000279014400011
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Doping-Dependent Nodal Fermi Velocity of the High-Temperature Superconductor Bi2Sr2CaCu2O8+delta Revealed Using High-Resolution Angle-Resolved Photoemission Spectroscopy
PHYSICAL REVIEW LETTERS
2010; 104 (20)
Abstract
The improved resolution of laser-based angle-resolved photoemission spectroscopy (ARPES) allows reliable access to fine structures in the spectrum. We present a systematic, doping-dependent study of a recently discovered low-energy kink in the nodal dispersion of Bi2Sr2CaCu2O(8+δ) (Bi-2212), which demonstrates the ubiquity and robustness of this kink in underdoped Bi-2212. The renormalization of the nodal velocity due to this kink becomes stronger with underdoping, revealing that the nodal Fermi velocity is nonuniversal, in contrast with assumed phenomenology. This is used together with laser ARPES measurements of the gap velocity (v2) to resolve discrepancies with thermal conductivity measurements.
View details for DOI 10.1103/PhysRevLett.104.207002
View details for Web of Science ID 000277945900042
View details for PubMedID 20867053
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Time-resolved photoemission of correlated electrons driven out of equilibrium
PHYSICAL REVIEW B
2010; 81 (16)
View details for DOI 10.1103/PhysRevB.81.165112
View details for Web of Science ID 000277217200040
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Strong energy-momentum dispersion of phonon-dressed carriers in the lightly doped band insulator SrTiO3
NEW JOURNAL OF PHYSICS
2010; 12
View details for DOI 10.1088/1367-2630/12/2/023004
View details for Web of Science ID 000274247300004
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Material and Doping Dependence of the Nodal and Antinodal Dispersion Renormalizations in Single- and Multilayer Cuprates
ADVANCES IN CONDENSED MATTER PHYSICS
2010
View details for DOI 10.1155/2010/968304
View details for Web of Science ID 000294023600001
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Finite-temperature spin dynamics and phase transitions in spin-orbital models
PHYSICAL REVIEW B
2009; 80 (18)
View details for DOI 10.1103/PhysRevB.80.180418
View details for Web of Science ID 000272310900023
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Band- and momentum-dependent electron dynamics in superconducting Ba(Fe1-xCox)(2)As-2 as seen via electronic Raman scattering
PHYSICAL REVIEW B
2009; 80 (18)
View details for DOI 10.1103/PhysRevB.80.180510
View details for Web of Science ID 000272310900035
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Collective d-wave exciton modes in the calculated Raman spectrum of Fe-based superconductors
PHYSICAL REVIEW B
2009; 80 (14)
View details for DOI 10.1103/PhysRevB.80.140512
View details for Web of Science ID 000271351500032
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A momentum-dependent perspective on quasiparticle interference in Bi2Sr2CaCu2O8+delta
NATURE PHYSICS
2009; 5 (10): 718-721
View details for DOI 10.1038/NPHYS1375
View details for Web of Science ID 000271185400010
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Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-T-c superconductors
NEW JOURNAL OF PHYSICS
2009; 11
View details for DOI 10.1088/1367-2630/11/9/093020
View details for Web of Science ID 000269819000006
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Resonant inelastic x-ray scattering in electronically quasi-zero-dimensional CuB2O4
PHYSICAL REVIEW B
2009; 80 (9)
View details for DOI 10.1103/PhysRevB.80.092509
View details for Web of Science ID 000270383000023
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Dependence of Band-Renormalization Effects on the Number of Copper Oxide Layers in Tl-Based Copper Oxide Superconductors Revealed by Angle-Resolved Photoemission Spectroscopy
PHYSICAL REVIEW LETTERS
2009; 103 (6)
Abstract
Here we report the first angle-resolved photoemission measurement on nearly optimally doped multilayer Tl-based superconducting cuprates (Tl-2212 and Tl-1223) and a comparison study to single-layer (Tl-2201) compound. A "kink" in the band dispersion is found in all three compounds but exhibits different momentum dependence for the single-layer and multilayer compounds, reminiscent to that of Bi-based cuprates. This layer number dependent renormalization effect strongly implies that the spin-resonance mode is unlikely to be responsible for the dramatic renormalization effect near the antinodal region.
View details for DOI 10.1103/PhysRevLett.103.067003
View details for Web of Science ID 000268809300056
View details for PubMedID 19792598
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Unusual Layer-Dependent Charge Distribution, Collective Mode Coupling, and Superconductivity in Multilayer Cuprate Ba2Ca3Cu4O8F2
PHYSICAL REVIEW LETTERS
2009; 103 (3)
Abstract
Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high Tc superconductor Ba2Ca3Cu4O8F2 (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO2 layers, respectively. For the states originating from two inequivalent CuO2 layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.
View details for DOI 10.1103/PhysRevLett.103.036403
View details for Web of Science ID 000268088300048
View details for PubMedID 19659301
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Evidence for weak electronic correlations in iron pnictides
PHYSICAL REVIEW B
2009; 80 (1)
View details for DOI 10.1103/PhysRevB.80.014508
View details for Web of Science ID 000268617100099
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Impact of an oxygen dopant in Bi2Sr2CaCu2O8+delta
EPL
2009; 86 (3)
View details for DOI 10.1209/0295-5075/86/37007
View details for Web of Science ID 000266427700029
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Probing the pairing symmetry of the iron pnictides with electronic Raman scattering
PHYSICAL REVIEW B
2009; 79 (17)
View details for DOI 10.1103/PhysRevB.79.174521
View details for Web of Science ID 000266501100111
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High-resolution angle-resolved photoemission studies of quasiparticle dynamics in graphite
PHYSICAL REVIEW B
2009; 79 (12)
View details for DOI 10.1103/PhysRevB.79.125438
View details for Web of Science ID 000264769300119
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Photoemission kinks and phonons in cuprates
NATURE
2008; 455 (7213): E6-E7
View details for DOI 10.1038/nature07364
View details for Web of Science ID 000259639700056
View details for PubMedID 18833217
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Uncovering a pressure-tuned electronic transition in Bi1.98Sr2.06Y0.68Cu2O8+delta using Raman scattering and x-ray diffraction
PHYSICAL REVIEW LETTERS
2008; 100 (21)
Abstract
We report pressure-tuned Raman and x-ray diffraction data of Bi(1.98.)Sr(2.06)Y(0.68)Cu(2)O(8+delta) revealing a critical pressure at 21 GPa with anomalies in electronic Raman background, electron-phonon coupling lambda, spectral weight transfer, density dependent behavior of phonons and magnons, and a compressibility change in the c axis. For the first time in a cuprate, mobile charge carriers, lattice, and magnetism all show anomalies at a distinct critical pressure in the same experimental setting. Furthermore, the spectral changes suggest that the critical pressure at 21 GPa is related to the critical point at optimal doping.
View details for DOI 10.1103/PhysRevLett.100.217003
View details for Web of Science ID 000256585500042
View details for PubMedID 18518627
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Charge dynamics of doped holes in high T-c cuprate superconductors: A clue from optical conductivity
PHYSICAL REVIEW LETTERS
2008; 100 (16)
Abstract
The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay between the electron correlation and electron-phonon interaction resolving the long standing mystery of the midinfrared band.
View details for DOI 10.1103/PhysRevLett.100.166401
View details for Web of Science ID 000255457600060
View details for PubMedID 18518226
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Superconductivity-induced self-energy evolution of the nodal electron of optimally doped Bi2Sr2Ca0.92Y0.08Cu2O8+delta
PHYSICAL REVIEW B
2008; 77 (14)
View details for DOI 10.1103/PhysRevB.77.140504
View details for Web of Science ID 000255457300008
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CuK-edge resonant inelastic x-ray scattering in edge-sharing cuprates
PHYSICAL REVIEW B
2008; 77 (10)
View details for DOI 10.1103/PhysRevB.77.104519
View details for Web of Science ID 000254542700115
- Polaronic Behavior and Electron-Phonon Coupling in High Temperature Cuprate Superconductors as Revealed from Angle-Resolved Photoemission Spectroscopy Treatise of High Temperature Superconductivity 2008
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Polaron coherence condensation as the mechanism for colossal magnetoresistance in layered manganites
PHYSICAL REVIEW B
2007; 76 (23)
View details for DOI 10.1103/PhysRevB.76.233102
View details for Web of Science ID 000251986500002
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Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212
NATURE
2007; 450 (7166): 81-84
Abstract
The superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (T(c)) in conventional BCS superconductors. In underdoped high-T(c) superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above T(c) (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above T(c) is one of the central questions in high-T(c) research. Although some experimental evidence suggests that the two gaps are distinct, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu-O bond direction (nodal direction), we found a gap that opens at T(c) and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu-O bond direction (antinodal region) measured in earlier experiments.
View details for DOI 10.1038/nature06219
View details for Web of Science ID 000250585800040
View details for PubMedID 17972881
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Hierarchy of multiple many-body interaction scales in high-temperature superconductors
PHYSICAL REVIEW B
2007; 75 (17)
View details for DOI 10.1103/PhysRevB.75.174506
View details for Web of Science ID 000246890500119
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Aspects of electron-phonon self-energy revealed from angle-resolved photoemission spectroscopy
PHYSICAL REVIEW B
2007; 75 (19)
View details for DOI 10.1103/PhysRevB.75.195116
View details for Web of Science ID 000246890800045
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Raman scattering for triangular lattices spin-1/2 Heisenberg antiferromagnets
International Conference on Highly Frustrated Magnetism
IOP PUBLISHING LTD. 2007
View details for DOI 10.1088/0953-8984/19/14/145243
View details for Web of Science ID 000245670300044
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Momentum-dependent light scattering in insulating cuprates
PHYSICAL REVIEW B
2007; 75 (2)
View details for DOI 10.1103/PhysRevB.75.020403
View details for Web of Science ID 000243895100007
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Band Renormalization Effect in Bi2Sr2Ca2Cu3O10+δ
High Tc Superconductors and Related Transition Metal Oxides
Springer Berlin Heidelberg. 2007: 227–236
View details for DOI 10.1007/978-3-540-71023-3_18
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Inelastic light scattering from correlated electrons
REVIEWS OF MODERN PHYSICS
2007; 79 (1): 175-233
View details for DOI 10.1103/RevModPhys.79.175
View details for Web of Science ID 000244867600005
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Distinct Fermi-momentum-dependent energy gaps in deeply underdoped Bi2212
SCIENCE
2006; 314 (5807): 1910-1913
Abstract
We used angle-resolved photoemission spectroscopy applied to deeply underdoped cuprate superconductors Bi2Sr2Ca(1-x)YxCu2O8 (Bi2212) to reveal the presence of two distinct energy gaps exhibiting different doping dependence. One gap, associated with the antinodal region where no coherent peak is observed, increased with underdoping, a behavior known for more than a decade and considered as the general gap behavior in the underdoped regime. The other gap, associated with the near-nodal regime where a coherent peak in the spectrum can be observed, did not increase with less doping, a behavior not previously observed in the single particle spectra. We propose a two-gap scenario in momentum space that is consistent with other experiments and may contain important information on the mechanism of high-transition temperature superconductivity.
View details for DOI 10.1126/science.1133411
View details for Web of Science ID 000242996800043
View details for PubMedID 17114172
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Anomalous Fermi-surface dependent pairing in a self-doped high-T-c superconductor
PHYSICAL REVIEW LETTERS
2006; 97 (23)
Abstract
We report the discovery of a self-doped multilayer high Tc superconductor Ba2Ca3Cu4O8F2 (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi-surface sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a Tc of 60 K, possessing simultaneously both electron- and hole-doped Fermi-surface sheets. Intriguingly, the Fermi-surface sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic (pi/a, pi/a) scattering.
View details for DOI 10.1103/PhysRevLett.97.236401
View details for Web of Science ID 000242708900037
View details for PubMedID 17280217
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Calculation of overdamped c-axis charge dynamics and the coupling to polar phonons in cuprate superconductors
PHYSICAL REVIEW B
2006; 74 (17)
View details for DOI 10.1103/PhysRevB.74.174524
View details for Web of Science ID 000242409000130
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Effects of pairing potential scattering on Fourier-transformed inelastic tunneling spectra of high-T-c cuprate superconductors with bosonic modes
PHYSICAL REVIEW LETTERS
2006; 97 (17)
Abstract
Recent scanning tunneling microscopy (STM) experimentally observed strong gap inhomogeneity in Bi2Sr2CaCu2O(8+delta) (BSCCO). We argue that disorder in the pair potential underlies the gap inhomogeneity, and investigate its role in the Fourier-transformed inelastic tunneling spectra as revealed in the STM. We find that the random pair potential induces unique q-space patterns in the local density of states (LDOS) of a d-wave superconductor. We consider the effects of electron coupling to various bosonic modes and find the pattern of LDOS modulation due to coupling to the B(1g) phonon mode to be consistent with the one observed in the inelastic electron tunnneling STM experiment in BSCCO. These results suggest strong electron-lattice coupling as an essential part of the superconducting state in high-Tc materials.
View details for DOI 10.1103/PhysRevLett.97.177001
View details for Web of Science ID 000241586800053
View details for PubMedID 17155496
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Sum rules for inelastic light scattering in the Hubbard model
International Conference on Strongly Correlated Electron Systems (SCES 05)
ELSEVIER SCIENCE BV. 2006: 650–653
View details for DOI 10.1016/j.physb.2006.01.186
View details for Web of Science ID 000238426600277
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Doping dependence of the coupling of electrons to bosonic modes in the single-layer high-temperature Bi2Sr2CuO6 superconductor
PHYSICAL REVIEW LETTERS
2006; 96 (15)
Abstract
A recent highlight in the study of high-T(c) superconductors is the observation of band renormalization or self-energy effects on the quasiparticles. This is seen in the form of kinks in the quasiparticle dispersions as measured by photoemission and interpreted as signatures of collective bosonic modes coupling to the electrons. Here we compare for the first time the self-energies in an optimally doped and strongly overdoped, nonsuperconducting single-layer Bi-cuprate (Bi2Sr2CuO6). In addition to the appearance of a strong overall weakening, we also find that the weight of the self-energy in the overdoped system shifts to higher energies. We present evidence that this is related to a change in the coupling to c-axis phonons due to the rapid change of the c-axis screening in this doping range.
View details for DOI 10.1103/PhysRevLett.96.157003
View details for Web of Science ID 000236969700057
View details for PubMedID 16712188
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Resonance mode in B-1g Raman scattering: A way to distinguish between spin-fluctuation and phonon-mediated d-wave superconductivity
PHYSICAL REVIEW B
2006; 73 (9)
View details for DOI 10.1103/PhysRevB.73.094512
View details for Web of Science ID 000236467100156
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Resonant enhancement of electronic Raman scattering
7th International Conference on Spectroscopies in Novel Superconductors (SNS 04)
PERGAMON-ELSEVIER SCIENCE LTD. 2006: 336–39
View details for DOI 10.1016/j.jpcs.2005.10.048
View details for Web of Science ID 000236746600083
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Fourier-transformed local density of states and tunneling into a d-wave superconductor with bosonic modes
PHYSICAL REVIEW B
2006; 73 (1)
View details for DOI 10.1103/PhysRevB.73.014511
View details for Web of Science ID 000235009000111
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Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites
NATURE
2005; 438 (7067): 474-478
Abstract
A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the 'd-wave' symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite 'Fermi arcs'. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.
View details for DOI 10.1038/nature04273
View details for Web of Science ID 000233458200044
View details for PubMedID 16306987
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Optical sum rules that relate to the potential energy of strongly correlated systems
PHYSICAL REVIEW LETTERS
2005; 94 (21)
Abstract
A class of sum rules for inelastic light scattering is developed. We show that the first moment of the nonresonant response provides information about the potential energy in strongly correlated systems. The polarization dependence of the sum rules provides information about the electronic excitations in different regions of the Brillouin zone. We determine the sum rule for the Falicov-Kimball model, which possesses a metal-insulator transition, and compare our results to the light scattering experiments in SmB(6).
View details for DOI 10.1103/PhysRevLett.94.216401
View details for Web of Science ID 000229543900032
View details for PubMedID 16090335
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Resonant electronic Raman scattering near a quantum critical point
International Conference on Strongly Correlated Electron Systems (SCES 04)
ELSEVIER SCIENCE BV. 2005: 705–707
View details for DOI 10.1016/j.physb.2005.01.200
View details for Web of Science ID 000229654400220
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A review of electron-phonon coupling seen in the high-T-c superconductors by angle-resolved photoemission studies (ARPES)
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
2005; 242 (1): 11-29
View details for DOI 10.1002/pssb.200404959
View details for Web of Science ID 000226603200006
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Review of Superconductivity in Complex Systems. Structure and Bonding, 114
J. Am. Chem. Soc.
2005; 128 (23): 7699
View details for DOI 10.1021/ja059826x
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Electronic Raman scattering in correlated materials: A treatment of nonresonant, mixed, and resonant scattering using dynamical mean-field theory
PHYSICAL REVIEW B
2005; 71 (4)
View details for DOI 10.1103/PhysRevB.71.045120
View details for Web of Science ID 000226736200041
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Interplay between the pseudogap and superconductivity in underdoped HgBa2CuO4+delta single crystals
PHYSICAL REVIEW B
2005; 71 (1)
View details for DOI 10.1103/PhysRevB.71.012506
View details for Web of Science ID 000226735100034
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Resonant enhancement of inelastic light scattering in strongly correlated materials
PHYSICAL REVIEW LETTERS
2004; 93 (13)
Abstract
We use dynamical mean field theory to find an exact solution for inelastic light scattering in strongly correlated materials such as those near a quantum-critical metal-insulator transition. We evaluate the results for q=0 (Raman) scattering and find that resonant effects can be quite large, and yield a double resonance, a significant enhancement of nonresonant scattering peaks, a joint resonance of both peaks when the incident photon frequency is on the order of U, and the appearance of an isosbestic point in all symmetry channels for an intermediate range of incident photon frequencies.
View details for DOI 10.1103/PhysRevLett.93.137402
View details for Web of Science ID 000224131400074
View details for PubMedID 15524756
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Coupling of the B-1g phonon to the antinodal electronic states of Bi2Sr2Ca0.92Y0.08Cu2O8+delta
PHYSICAL REVIEW LETTERS
2004; 93 (11)
Abstract
Angle-resolved photoemission spectroscopy on optimally doped Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+delta) uncovers a coupling of the electronic bands to a 40 meV mode in an extended k-space region away from the nodal direction, leading to a new interpretation of the strong renormalization of the electronic structure seen in Bi2212. Phenomenological agreements with neutron and Raman experiments suggest that this mode is the B(1g) oxygen bond-buckling phonon. A theoretical calculation based on this assignment reproduces the electronic renormalization seen in the data.
View details for DOI 10.1103/PhysRevLett.93.117003
View details for Web of Science ID 000223794400050
View details for PubMedID 15447370
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Anisotropic electron-phonon interaction in the cuprates
PHYSICAL REVIEW LETTERS
2004; 93 (11)
Abstract
We explore manifestations of electron-phonon coupling on the electron spectral function for two phonon modes in the cuprates exhibiting strong renormalizations with temperature and doping. Applying simple symmetry considerations and kinematic constraints, we find that the out-of-plane, out-of-phase O buckling mode (B(1g)) involves small momentum transfers and couples strongly to electronic states near the antinode while the in-plane Cu-O breathing modes involve large momentum transfers and couples strongly to nodal electronic states. Band renormalization effects are found to be strongest in the superconducting state near the antinode, in full agreement with angle-resolved photoemission spectroscopy data.
View details for DOI 10.1103/PhysRevLett.93.117004
View details for Web of Science ID 000223794400051
View details for PubMedID 15447371
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Critical current peaks at 3B(Phi) in superconductors with columnar defects: Recrystallizing the interstitial glass
PHYSICAL REVIEW LETTERS
2004; 93 (6)
Abstract
The role of commensurability and the interplay of correlated disorder and interactions on vortex dynamics in the presence of columnar pins is studied via molecular dynamics simulations. Simulations of dynamics reveal substantial caging effects and a nonmonotonic dependence of the critical current with enhancements near integer values of the matching field Bphi and 3Bphi in agreement with experiments on the cuprates. We find qualitative differences in the phase diagram for small and large values of the matching field.
View details for DOI 10.1103/PhysRevLett.93.067002
View details for Web of Science ID 000223138200043
View details for PubMedID 15323655
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Optical symmetries and anisotropic transport in high-T-c superconductors
PHYSICAL REVIEW B
2003; 68 (9)
View details for DOI 10.1103/PhysRevB.68.094503
View details for Web of Science ID 000185717600084
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Inelastic x-ray scattering as a probe of electronic correlations
PHYSICAL REVIEW B
2003; 68 (7)
View details for DOI 10.1103/PhysRevB.68.075105
View details for Web of Science ID 000185241200034
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Nonresonant inelastic light scattering in the Hubbard model
PHYSICAL REVIEW B
2003; 67 (15)
View details for DOI 10.1103/PhysRevB.67.155102
View details for Web of Science ID 000182741400027
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Inelastic X-ray scattering in correlated Mott insulators
PHYSICAL REVIEW LETTERS
2003; 90 (6)
Abstract
We calculate the inelastic light scattering from x rays, which allows the photon to transfer both energy and momentum to the strongly correlated charge excitations. We find that the charge-transfer peak and the low-energy peak both broaden and disperse through the Brillouin zone similar to what is seen in experiments in materials such as Ca2CuO2Cl2.
View details for DOI 10.1103/PhysRevLett.90.067402
View details for Web of Science ID 000181015900050
View details for PubMedID 12633327
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Inelastic light scattering and the correlated metal-insulator transition
International Conference on Strongly Correlated Electron Systems (SCES 2002)
WYDAWNICTWO UNIWERSYTETU JAGIELLONSKIEGO. 2003: 737–48
View details for Web of Science ID 000181544200087
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Inelastic light scattering and the correlated metal-insulator transition
NATO Advanced Research Workshop on Concepts in Electron Correlation
SPRINGER. 2003: 115–122
View details for Web of Science ID 000186817000011
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Observation of an unconventional metal-insulator transition in overdoped CuO2 compounds
PHYSICAL REVIEW LETTERS
2002; 89 (10)
Abstract
The electron dynamics in the normal state of Bi(2)Sr(2)CaCu(2)O(8+delta) is studied by inelastic light scattering over a wide range of doping. A strong anisotropy of the electron relaxation is found which cannot be explained by single-particle properties alone. The results strongly indicate the presence of an unconventional quantum-critical metal-insulator transition where "hot" (antinodal) quasiparticles become insulating while "cold" (nodal) quasiparticles remain metallic. A phenomenology is developed which allows a quantitative understanding of the Raman results and provides a scenario which links single- and many-particle properties.
View details for DOI 10.1103/PhysRevLett.89.107003
View details for Web of Science ID 000177582600043
View details for PubMedID 12225217
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Exact theory for electronic Raman scattering of correlated materials in infinite dimensions
PHYSICAL REVIEW B
2001; 64 (23)
View details for DOI 10.1103/PhysRevB.64.233114
View details for Web of Science ID 000172867900014
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B-1g Raman scattering through a quantum critical point
12th School on Phase Transitions and Critical Phenomena to the Scientific Community
WYDAWNICTWO UNIWERSYTETU JAGIELLONSKIEGO. 2001: 3219–31
View details for Web of Science ID 000172375300005
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Raman scattering through a metal-insulator transition
PHYSICAL REVIEW B
2001; 64 (12)
View details for Web of Science ID 000171244400033
- Non-Resonant Raman Scattering Through a Metal-Insulator Transition: An Exact Analysis of the Falicov-Kimball Model Proceedings of the Workshop on Soft Matter Theory 2001: 149–60
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Collective spin fluctuation mode and Raman scattering in superconducting cuprates
PHYSICAL REVIEW B
2000; 62 (22): 15204-15207
View details for Web of Science ID 000165883800079
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A consistent picture of electronic Raman scattering and infrared conductivity in the cuprates
International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VI
ELSEVIER SCIENCE BV. 2000: 2229–2230
View details for Web of Science ID 000165856000060
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The role of splayed disorder and channel flow on the dynamics of driven 3D vortices
International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VI
ELSEVIER SCIENCE BV. 2000: 1219–1220
View details for Web of Science ID 000165855700209
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Unconventional electronic Raman spectra of borocarbide superconductors
International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VI
ELSEVIER SCIENCE BV. 2000: 2259–2260
View details for Web of Science ID 000165856000075
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Collective modes and electronic Raman scattering in the cuprates
International Conference on Materials and Mechanisms of Superconductivity High Temperature Superconductors VI
ELSEVIER SCIENCE BV. 2000: 2265–2266
View details for Web of Science ID 000165856000078
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Contribution to the quasiparticle inelastic lifetime from paramagnons in disordered superconductors
PHYSICAL REVIEW B
2000; 62 (1): 682-685
View details for Web of Science ID 000088037000107
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Consistent picture of electronic Raman scattering and infrared conductivity in the cuprates
PHYSICAL REVIEW B
2000; 61 (2): 1490-1494
View details for Web of Science ID 000085760000092
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Physical origin of the buckling in CuO2: Electron-phonon coupling and Raman spectra
PHYSICAL REVIEW B
1999; 60 (13): 9836-9844
View details for Web of Science ID 000083079200102
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Neutron scattering and the B-1g phonon in the cuprates
PHYSICAL REVIEW B
1999; 59 (22): 14618-14623
View details for Web of Science ID 000080780700059
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Theory of electronic Raman scattering in nearly antiferromagnetic Fermi liquids
PHYSICAL REVIEW B
1999; 59 (9): 6411-6420
View details for Web of Science ID 000079254300062
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Neutron Scattering and the B1g Phonon in the Cuprates
Phys. Review B
1999; 59: 14618
View details for DOI 10.1103/PhysRevB.59.14618
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Theory of Raman Scattering in a Nearly Antiferromagnetic Fermi Liquid
Phys. Review B
1999: 6411
View details for DOI 10.1103/PhysRevB.59.6411
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Electronic Raman scattering in nearly antiferromagnetic Fermi liquids
International Conference on Spectroscopies in Novel Superconductors (SNS'97)
PERGAMON-ELSEVIER SCIENCE LTD. 1998: 1972–75
View details for Web of Science ID 000077460500073
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Evidence for magnetic pseudoscaling in overdoped La2-xSrxCuO4
PHYSICAL REVIEW B
1998; 57 (18): R11077-R11080
View details for Web of Science ID 000073585200016
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Enhanced electron-phonon coupling and its irrelevance to high T-c superconductivity
SOLID STATE COMMUNICATIONS
1998; 108 (7): 407-411
View details for Web of Science ID 000076645400002
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Raman Scattering in a Nearly Antiferromagnetic Fermi Liquid
Journal of Physics and Chemistry Solids
1998; 59 (10-12): 1972-1975
View details for DOI 10.1016/S0022-3697(98)00158-9
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Extended impurity potential in a d(x2-y2) superconductor
PHYSICAL REVIEW B
1997; 56 (5): 2360-2363
View details for Web of Science ID A1997XQ61900022
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Raman scattering in cuprate superconductors
INTERNATIONAL JOURNAL OF MODERN PHYSICS B
1997; 11 (18): 2093-2118
View details for Web of Science ID A1997XR51900001
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Superconducting gap anisotropy vs doping level in high-T-c cuprates - Comment
PHYSICAL REVIEW LETTERS
1997; 78 (25): 4891-4891
View details for Web of Science ID A1997XJ26900057
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Comment on "Superconducting Gap Anisotropy vs. Doping Level in High-Tc Cuprates
Phys. Rev. Lett.
1997; 78: 4891
View details for DOI 10.1103/PhysRevLett.78.4891
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Electronic Raman scattering in superconductors as a probe of anisotropic electron pairing (vol 51, pg 16 336, 1995)
PHYSICAL REVIEW B
1996; 54 (21): 15547-15547
View details for Web of Science ID A1996VY20100107
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Multiband electronic Raman scattering in bilayer superconductors
PHYSICAL REVIEW B
1996; 54 (17): 12523-12534
View details for Web of Science ID A1996VT68100106
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Magnetic pair breaking in disordered superconducting films
PHYSICAL REVIEW B
1996; 53 (1): 359-364
View details for Web of Science ID A1996TR04100062
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Role of symmetry in Raman spectroscopy of unconventional superconductors
Conference on Spectroscopic Studies of Superconductors
SPIE - INT SOC OPTICAL ENGINEERING. 1996: 230–241
View details for Web of Science ID A1996BG07T00023
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Phase diagram for splay glass superconductivity
PHYSICAL REVIEW LETTERS
1995; 75 (26): 4768-4771
View details for Web of Science ID A1995TL67700013
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Study of k-dependent electronic properties in cuprate superconductors using Raman spectroscopy
Conference on Spectroscopies in Novel Superconductors
PERGAMON-ELSEVIER SCIENCE LTD. 1995: 1841–42
View details for Web of Science ID A1995TL54700082
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Raman scattering in disordered unconventional superconductors
Conference on Spectroscopies in Novel Superconductors
PERGAMON-ELSEVIER SCIENCE LTD. 1995: 1711–12
View details for Web of Science ID A1995TL54700034
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ELECTRONIC RAMAN-SCATTERING AS A PROBE OF ANISOTROPIC ELECTRON PAIRING
University-of-Miami Workshop on High-Temperature Superconductivity - Physical Properties and Mechanisms
SPRINGER/PLENUM PUBLISHERS. 1995: 421–24
View details for Web of Science ID A1995RU78500008
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ELECTRONIC RAMAN-SCATTERING IN SUPERCONDUCTORS AS A PROBE OF ANISOTROPIC ELECTRON PAIRING
PHYSICAL REVIEW B
1995; 51 (22): 16336-16357
View details for Web of Science ID A1995RD55200073
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THEORY OF ELECTRONIC RAMAN-SCATTERING IN DISORDERED UNCONVENTIONAL SUPERCONDUCTORS
PHYSICAL REVIEW LETTERS
1995; 74 (21): 4313-4316
View details for Web of Science ID A1995QZ23600054
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EFFECT OF COMPETITION BETWEEN POINT AND COLUMNAR DISORDER ON THE BEHAVIOR OF FLUX LINES IN (1+1) DIMENSIONS (VOL 50, PG 13625, 1994)
PHYSICAL REVIEW B
1995; 51 (13): 8689-8689
View details for Web of Science ID A1995QR97800098
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Erratum: Effect of competition between point and columnar disorder on the behavior of flux lines in (1+1) dimensions
Physical review. B, Condensed matter
1995; 51 (13): 8689-?
View details for PubMedID 9986943
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CHARGE-TRANSFER FLUCTUATION, D-WAVE SUPERCONDUCTIVITY, AND THE B-1G RAMAN PHONON IN CUPRATES
PHYSICAL REVIEW B
1995; 51 (1): 505-514
View details for Web of Science ID A1995QB37700060
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ELECTRONIC RAMAN-SCATTERING IN HIGH-T-C SUPERCONDUCTORS
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS
1994; 235: 57-58
View details for Web of Science ID A1994QA39000019
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EFFECT OF COMPETITION BETWEEN POINT AND COLUMNAR DISORDER ON THE BEHAVIOR OF FLUX LINES IN (1+1)-DIMENSIONS
PHYSICAL REVIEW B
1994; 50 (18): 13625-13631
View details for Web of Science ID A1994PT41000062
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SYMMETRY DEPENDENCE OF PHONON LINE-SHAPES IN SUPERCONDUCTORS WITH ANISOTROPIC GAPS
PHYSICAL REVIEW B
1994; 50 (14): 10287-10293
View details for Web of Science ID A1994PL95100066
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ELECTRONIC RAMAN-SCATTERING IN HIGH-T(C) SUPERCONDUCTORS - A PROBE OF D(X2-Y2) PAIRING - REPLY
PHYSICAL REVIEW LETTERS
1994; 72 (20): 3291-3291
View details for Web of Science ID A1994NL60900044
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Devereaux et al. reply.
Physical review letters
1994; 72 (20): 3291-?
View details for PubMedID 10056159
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GAUGE-INVARIANT RESPONSE OF A SUPERCONDUCTOR WITH DX(2)-Y(2) SYMMETRY - APPLICATION TO ELECTRONIC RAMAN-SCATTERING
20th International Conference on Low Temperature Physics
ELSEVIER SCIENCE BV. 1994: 1531–1532
View details for Web of Science ID A1994NC27500090
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ELECTRONIC RAMAN-SCATTERING IN HIGH-T(C) SUPERCONDUCTORS - A PROBE OF DX2-Y2 PAIRING
PHYSICAL REVIEW LETTERS
1994; 72 (3): 396-399
View details for Web of Science ID A1994MR49200022
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Devereaux et al. Reply
Physical Review Letters
1994; 72 (20): 3291
View details for DOI 10.1103/PhysRevLett.72.3291
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Investigation of the pairing symmetry in high-T-c superconductors by electronic Raman scattering
14th International Conference on Raman Spectroscopy
JOHN WILEY & SONS LTD. 1994: 326–327
View details for Web of Science ID A1994BD55D00143
- Electronic Investigation of the Pairing Symmetry in High-Tc Superconductors by Electronic Raman Scatteringattering Proceedings of the Fourteenth International Conference on Raman Spectroscopy 1994: 327
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MULTIPLE ANDREEV SCATTERING IN SUPERCONDUCTOR NORMAL-METAL SUPERCONDUCTOR JUNCTIONS AS A TEST FOR ANISOTROPIC ELECTRON PAIRING
PHYSICAL REVIEW B
1993; 47 (21): 14638-14641
View details for Web of Science ID A1993LF72900102
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THEORY FOR THE EFFECTS OF IMPURITIES ON THE RAMAN-SPECTRA OF SUPERCONDUCTORS .2. TEMPERATURE-DEPENDENCE AND INFLUENCE OF FINAL-STATE INTERACTIONS
PHYSICAL REVIEW B
1993; 47 (9): 5230-5238
View details for Web of Science ID A1993KQ09900052
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NUCLEAR-SPIN RELAXATION IN STRONGLY DISORDERED SUPERCONDUCTORS
ZEITSCHRIFT FUR PHYSIK B-CONDENSED MATTER
1993; 90 (1): 65-68
View details for Web of Science ID A1993KB32200008
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THEORY FOR THE EFFECTS OF IMPURITIES ON THE RAMAN-SPECTRA OF SUPERCONDUCTORS
PHYSICAL REVIEW B
1992; 45 (22): 12965-12975
View details for Web of Science ID A1992HZ24200043
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QUASI-PARTICLE INELASTIC LIFETIMES IN DISORDERED SUPERCONDUCTING FILMS
PHYSICAL REVIEW B
1991; 44 (9): 4587-4600
View details for Web of Science ID A1991GD96700063
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POWER-LAW TEMPERATURE-DEPENDENCE OF THE INELASTIC-SCATTERING RATE IN DISORDERED SUPERCONDUCTORS
PHYSICAL REVIEW B
1991; 43 (4): 3736-3739
View details for Web of Science ID A1991FF08600090
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Quasiparticle Lifetimes in Disordered Superconducting Film
Phys. Review B
1991; 44 (9): 4587-4600
View details for DOI 10.1103/PhysRevB.44.4587
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DISORDER ENHANCEMENT OF QUASIPARTICLE LIFETIMES IN SUPERCONDUCTORS
JOURNAL OF LOW TEMPERATURE PHYSICS
1989; 77 (5-6): 319-326
View details for Web of Science ID A1989CD28200002
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ELECTROMAGNETIC RESPONSE OF DISORDERED SUPERCONDUCTORS
PHYSICAL REVIEW B
1989; 39 (4): 2072-2083
View details for Web of Science ID A1989T144500012