- Enhanced correlations and superconductivity in weakly interacting partially flat-band systems: A determinantal quantum Monte Carlo study PHYSICAL REVIEW B 2019; 99 (23)
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
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
Three-dimensional collective charge excitations in electron-doped copper oxide superconductors.
2018; 563 (7731): 374–78
High-temperature copper oxide superconductors consist of stacked CuO2 planes, with electronic band structures and magnetic excitations that are primarily two-dimensional1,2, but with superconducting coherence that is three-dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, which has been found to be incoherent in the normal state3,4 within the limited range of momenta accessible by optics. Here we use resonant inelastic X-ray scattering to explore the charge dynamics across all three dimensions of the Brillouin zone. Polarization analysis of recently discovered collective excitations (modes) in electron-doped copper oxides5-7 reveals their charge origin, that is, without mixing with magnetic components5-7. The excitations disperse along both the in-plane and out-of-plane directions, revealing its three-dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the distance between neighbouring CuO2 planesrather than to the crystallographic c-axis lattice constant, suggesting that the interplane Coulomb interaction is responsible for the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought 'acoustic plasmon', which is a branch of distinct charge collective modes predicted for layered systems8-12 and argued to play a substantial part in mediating high-temperature superconductivity10-12.
View details for PubMedID 30429543
- Dispersion, damping, and intensity of spin excitations in the monolayer (Bi,Pb)(2)(Sr,La)(2)CuO6+delta cuprate superconductor family PHYSICAL REVIEW B 2018; 98 (14)
- Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model PHYSICAL REVIEW LETTERS 2018; 120 (24)
- Resonant inelastic x-ray scattering studies of magnons and bimagnons in the lightly doped cuprate La2-xSrxCuO4 PHYSICAL REVIEW B 2018; 97 (15)
- Breakdown of the Migdal-Eliashberg theory: A determinant quantum Monte Carlo study PHYSICAL REVIEW B 2018; 97 (14)
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
Numerical evidence of fluctuating stripes in the normal state of high-Tc cuprate superconductors
2017; 358 (6367): 1161-+
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
- Doping dependence of ordered phases and emergent quasiparticles in the doped Hubbard-Holstein model PHYSICAL REVIEW B 2017; 96 (20)
- 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)
- Effects of an additional conduction band on the singlet-antiferromagnet competition in the periodic Anderson model PHYSICAL REVIEW B 2017; 95 (23)
- Characterizing the three-orbital Hubbard model with determinant quantum Monte Carlo PHYSICAL REVIEW B 2016; 93 (15)
Photoinduced doping in heterostructures of graphene and boron nitride
2014; 9 (5): 348–52
The design of stacks of layered materials in which adjacent layers interact by van der Waals forces has enabled the combination of various two-dimensional crystals with different electrical, optical and mechanical properties as well as the emergence of novel physical phenomena and device functionality. Here, we report photoinduced doping in van der Waals heterostructures consisting of graphene and boron nitride layers. It enables flexible and repeatable writing and erasing of charge doping in graphene with visible light. We demonstrate that this photoinduced doping maintains the high carrier mobility of the graphene/boron nitride heterostructure, thus resembling the modulation doping technique used in semiconductor heterojunctions, and can be used to generate spatially varying doping profiles such as p-n junctions. We show that this photoinduced doping arises from microscopically coupled optical and electrical responses of graphene/boron nitride heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene.
View details for DOI 10.1038/nnano.2014.60
View details for Web of Science ID 000336235800010
View details for PubMedID 24727687