Jiarui Li

All Publications

• The classical-to-quantum crossover in the strain-induced ferroelectric transition in SrTiO3 membranes. Nature communications Li, J., Lee, Y., Choi, Y., Kim, J. W., Thompson, P., Crust, K. J., Xu, R., Hwang, H. Y., Ryan, P. J., Lee, W. S. 2025; 16 (1): 4445

  Abstract

  Mechanical strain presents an effective control over symmetry-breaking phase transitions. In quantum paraelectric SrTiO3, strain can induce ferroelectric order via modification of the local Ti potential energy landscape. However, brittle bulk materials can only withstand limited strain range (~0.1%). Taking advantage of nanoscopically-thin freestanding membranes, we demonstrate an in-situ strain-induced reversible ferroelectric transition in freestanding SrTiO3 membranes. We measure the ferroelectric order by detecting the local anisotropy of the Ti 3d orbital signature using X-ray linear dichroism at the Ti-K pre-edge, while the strain is determined by X-ray diffraction. With reduced thickness, the SrTiO3 membranes remain elastic with >1% tensile strain cycles. A robust displacive ferroelectricity appears beyond a temperature-dependent critical strain. Interestingly, we discover a crossover from a classical ferroelectric transition to a quantum regime at low temperatures, which enhances strain-induced ferroelectricity. Our results offer new opportunities to strain engineer functional properties in low dimensional quantum materials and provide new insights into the role of ferroelectric fluctuations in quantum paraelectric SrTiO3.

  View details for DOI 10.1038/s41467-025-59517-4

  View details for PubMedID 40360489

  View details for PubMedCentralID PMC12075646

• Doping Dependence of 2-Spinon Excitations in the Doped 1D Cuprate Ba_{2}CuO_{3+δ}. Physical review letters Li, J., Jost, D., Tang, T., Wang, R., Zhong, Y., Chen, Z., Garcia-Fernandez, M., Pelliciari, J., Bisogni, V., Moritz, B., Zhou, K., Wang, Y., Devereaux, T. P., Lee, W. S., Shen, Z. X. 2025; 134 (14): 146501

  Abstract

  Recent photoemission experiments on the quasi-one-dimensional Ba-based cuprates suggest that doped holes experience an attractive potential not captured using the simple Hubbard model. This observation has garnered significant attention due to its potential relevance to Cooper pair formation in high-T_{c} cuprate superconductors. To scrutinize this assertion, we examined signatures of such an attractive potential in doped 1D cuprates Ba_{2}CuO_{3+δ} by measuring the dispersion of the 2-spinon excitations using Cu L_{3}-edge resonant inelastic x-ray scattering (RIXS). Upon doping, the 2-spinon excitations appear to weaken, with a shift of the minimal position corresponding to the nesting vector of the Fermi points, q_{F}. Notably, we find that the energy scale of the 2-spinons near the Brillouin zone boundary is substantially softened compared to that predicted by the Hubbard model in one dimension. Such a discrepancy implies missing ingredients, which lends support for the presence of an additional attractive potential between holes.

  View details for DOI 10.1103/PhysRevLett.134.146501

  View details for PubMedID 40279597

• Signatures of polarized chiral spin disproportionation in rare earth nickelates. Nature communications Li, J., Green, R. J., Domínguez, C., Levitan, A., Tseng, Y., Catalano, S., Fowlie, J., Sutarto, R., Rodolakis, F., Korol, L., McChesney, J. L., Freeland, J. W., Van der Marel, D., Gibert, M., Comin, R. 2024; 15 (1): 7427

  Abstract

  In rare earth nickelates (RENiO3), electron-lattice coupling drives a concurrent metal-to-insulator and bond disproportionation phase transition whose microscopic origin has long been the subject of active debate. Of several proposed mechanisms, here we test the hypothesis that pairs of self-doped ligand holes spatially condense to provide local spin moments that are antiferromagnetically coupled to Ni spins. These singlet-like states provide a basis for long-range bond and spiral spin order. Using magnetic resonant X-ray scattering on NdNiO3 thin films, we observe the chiral nature of the spin-disproportionated state, with spin spirals propagating along the crystallographic (101)ortho direction. These spin spirals are found to preferentially couple to X-ray helicity, establishing the presence of a hitherto-unobserved macroscopic chirality. The presence of this chiral magnetic configuration suggests a potential multiferroic coupling between the noncollinear magnetic arrangement and improper ferroelectric behavior as observed in prior studies on NdNiO3 (101)ortho films and RENiO3 single crystals. Experimentally-constrained theoretical double-cluster calculations confirm the presence of an energetically stable spin-disproportionated state with Zhang-Rice singlet-like combinations of Ni and ligand moments.

  View details for DOI 10.1038/s41467-024-51576-3

  View details for PubMedID 39198459

  View details for PubMedCentralID PMC11358138

• Sudden Collapse of Magnetic Order in Oxygen-Deficient Nickelate Films PHYSICAL REVIEW LETTERS Li, J., Green, R. J., Zhang, Z., Sutarto, R., Sadowski, J. T., Zhu, Z., Zhang, G., Zhou, D., Sun, Y., He, F., Ramanathan, S., Comin, R. 2021; 126 (18): 187602

  Abstract

  Antiferromagnetic order is a common and robust ground state in the parent (undoped) phase of several strongly correlated electron systems. The progressive weakening of antiferromagnetic correlations upon doping paves the way for a variety of emergent many-electron phenomena including unconventional superconductivity, colossal magnetoresistance, and collective charge-spin-orbital ordering. In this study, we explored the use of oxygen stoichiometry as an alternative pathway to modify the coupled magnetic and electronic ground state in the family of rare earth nickelates (RENiO_{3-x}). Using a combination of x-ray spectroscopy and resonant soft x-ray magnetic scattering, we find that, while oxygen vacancies rapidly alter the electronic configuration within the Ni and O orbital manifolds, antiferromagnetic order is remarkably robust to substantial levels of carrier doping, only to suddenly collapse beyond 0.21 e^{-}/Ni without an accompanying structural transition. Our work demonstrates that ordered magnetism in RENiO_{3-x} is mostly insensitive to carrier doping up to significant levels unseen in other transition-metal oxides. The sudden collapse of ordered magnetism upon oxygen removal may provide a new mechanism for solid-state magnetoionic switching and new applications in antiferromagnetic spintronics.

  View details for DOI 10.1103/PhysRevLett.126.187602

  View details for Web of Science ID 000652838100012

  View details for PubMedID 34018782

• Distinction between pristine and disorder-perturbed charge density waves in ZrTe3 NATURE COMMUNICATIONS Yue, L., Xue, S., Li, J., Hu, W., Barbour, A., Zheng, F., Wang, L., Feng, J., Wilkins, S. B., Mazzoli, C., Comin, R., Li, Y. 2020; 11 (1): 98

  Abstract

  Charge density waves (CDWs) in the cuprate high-temperature superconductors have evoked much interest, yet their typical short-range nature has raised questions regarding the role of disorder. Here we report a resonant X-ray diffraction study of ZrTe[Formula: see text], a model CDW system, with focus on the influence of disorder. Near the CDW transition temperature, we observe two independent signals that arise concomitantly, only to become clearly separated in momentum while developing very different correlation lengths in the well-ordered state that is reached at a distinctly lower temperature. Anomalously slow dynamics of mesoscopic charge domains are further found near the transition temperature, in spite of the expected strong thermal fluctuations. Our observations signify the presence of distinct experimental fingerprints of pristine and disorder-perturbed CDWs. We discuss the latter also in the context of Friedel oscillations, which we argue might promote CDW formation via a self-amplifying process.

  View details for DOI 10.1038/s41467-019-13813-y

  View details for Web of Science ID 000511967900002

  View details for PubMedID 31911603

  View details for PubMedCentralID PMC6946692

• Scale-invariant magnetic textures in the strongly correlated oxide NdNiO3 NATURE COMMUNICATIONS Li, J., Pelliciari, J., Mazzoli, C., Catalano, S., Simmons, F., Sadowski, J. T., Levitan, A., Gibert, M., Carlson, E., Triscone, J., Wilkins, S., Comin, R. 2019; 10: 4568

  Abstract

  Strongly correlated quantum solids are characterized by an inherently granular electronic fabric, with spatial patterns that can span multiple length scales in proximity to a critical point. Here, we use a resonant magnetic X-ray scattering nanoprobe with sub-100 nm spatial resolution to directly visualize the texture of antiferromagnetic domains in NdNiO3. Surprisingly, our measurements reveal a highly textured magnetic fabric, which we show to be robust and nonvolatile even after thermal erasure across its ordering temperature. The scale-free distribution of antiferromagnetic domains and its non-integral dimensionality point to a hitherto-unobserved magnetic fractal geometry in this system. These scale-invariant textures directly reflect the continuous nature of the magnetic transition and the proximity of this system to a critical point. The present study not only exposes the near-critical behavior in rare earth nickelates but also underscores the potential for X-ray scattering nanoprobes to image the multiscale signatures of criticality near a critical point.

  View details for DOI 10.1038/s41467-019-12502-0

  View details for Web of Science ID 000490117800001

  View details for PubMedID 31615992

  View details for PubMedCentralID PMC6794273

• Superconductivity and normal-state transport in compressively strained La2PrNi2O7 thin films. Nature materials Liu, Y., Ko, E. K., Tarn, Y., Bhatt, L., Li, J., Thampy, V., Goodge, B. H., Muller, D. A., Raghu, S., Yu, Y., Hwang, H. Y. 2025

  Abstract

  The discovery of superconductivity under high pressure in Ruddlesden-Popper phases of bulk nickelates has sparked great interest in stabilizing ambient-pressure superconductivity in the thin-film form using epitaxial strain. Recently, signs of superconductivity have been observed in compressively strained bilayer nickelate thin films with an onset temperature exceeding 40 K, although with broad, two-step-like transitions. Here we report the intrinsic superconductivity and normal-state transport properties in compressively strained La2PrNi2O7 thin films, achieved through a combination of isovalent Pr substitution, growth optimization and precision ozone annealing. The superconducting onset occurs above 48 K, with zero resistance reached above 30 K, and the critical current density at 1.4 K is 100-fold larger than previous reports. The normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour, and other phenomenological similarities to transport in overdoped cuprates suggest parallels in their emergent properties.

  View details for DOI 10.1038/s41563-025-02258-y

  View details for PubMedID 40442446

  View details for PubMedCentralID 10951943

• Molecular H2as the Reducing Agent in Low-Temperature Oxide Reduction Using Calcium Hydride. Journal of the American Chemical Society Wang, J., Yu, Y., Abdelkawy, A., Li, J., Li, J., Yang, J., Ko, E. K., Lee, Y., Thampy, V., Cui, Y., Todorova, M., Neugebauer, J., Hwang, H. Y. 2025

  Abstract

  Low-temperature synthesis is crucial for advancing sustainable manufacturing and accessing novel metastable phases. Metal hydrides have shown great potential in facilitating the reduction of oxides at low temperatures, yet the underlying mechanism─whether driven by H-, H2, or atomic H─remains unclear. In this study, we employ in situ electrical transport measurements and first-principles calculations to investigate the CaH2-driven reduction kinetics in epitaxial alpha-Fe2O3 thin films. Intriguingly, samples in direct contact with or separated from CaH2 powders exhibit similar apparent activation energies for H2 reduction, although direct contact significantly increases the reduction rate. These findings indicate that molecular H2 is the dominant reducing species in the low-temperature reduction of oxides using CaH2, with a key aspect of the hydrides' superior reducing power attributed to their ability to eliminate residual moisture. This work underscores the critical role of moisture control in enabling effective low-temperature oxide reduction for advanced material synthesis.

  View details for DOI 10.1021/jacs.4c17825

  View details for PubMedID 39807810

• Signatures of ambient pressure superconductivity in thin film La3Ni2O7. Nature Ko, E. K., Yu, Y., Liu, Y., Bhatt, L., Li, J., Thampy, V., Kuo, C. T., Wang, B. Y., Lee, Y., Lee, K., Lee, J. S., Goodge, B. H., Muller, D. A., Hwang, H. Y. 2024

  Abstract

  Recently, the bilayer nickelate La3Ni2O7 has been discovered as a new superconductor with transition temperature Tc near 80 K under high pressure1-3. Despite extensive theoretical and experimental work to understand the nature of its superconductivity4-29, the requirement of extreme pressure restricts the use of many experimental probes and limits its application potential. Here, we present signatures of superconductivity in La3Ni2O7 thin films at ambient pressure, facilitated by the application of epitaxial compressive strain. The onset Tc varies approximately from 26 K to 42 K, with higher Tc values correlating with smaller in-plane lattice constants. We observed the co-existence of other Ruddlesden-Popper phases within the films and dependence of transport behavior with ozone annealing, suggesting that the observed low zero resistance Tc of around 2 K can be attributed to stacking defects, grain boundaries, and oxygen stoichiometry. This finding initiates numerous opportunities to stabilize and study superconductivity in bilayer nickelates at ambient pressure, and to facilitate the broad understanding of the ever-growing number of high temperature and unconventional superconductors in the transition metal oxides.

  View details for DOI 10.1038/s41586-024-08525-3

  View details for PubMedID 39701131

• Author Correction: Highly confined epsilon-near-zero and surface phonon polaritons in SrTiO3membranes. Nature communications Xu, R., Crassee, I., Bechtel, H. A., Zhou, Y., Bercher, A., Korosec, L., Rischau, C. W., Teyssier, J., Crust, K. J., Lee, Y., Gilbert Corder, S. N., Li, J., Dionne, J. A., Hwang, H. Y., Kuzmenko, A. B., Liu, Y. 2024; 15 (1): 8545

  View details for DOI 10.1038/s41467-024-52983-2

  View details for PubMedID 39358377

• Magnetic excitations in strained infinite-layer nickelate PrNiO2films. Nature communications Gao, Q., Fan, S., Wang, Q., Li, J., Ren, X., Bialo, I., Drewanowski, A., Rothenbuhler, P., Choi, J., Sutarto, R., Wang, Y., Xiang, T., Hu, J., Zhou, K., Bisogni, V., Comin, R., Chang, J., Pelliciari, J., Zhou, X. J., Zhu, Z. 2024; 15 (1): 5576

  Abstract

  Strongly correlated materials respond sensitively to external perturbations such as strain, pressure, and doping. In the recently discovered superconducting infinite-layer nickelates, the superconducting transition temperature can be enhanced via only~1% compressive strain-tuning with the root of such enhancement still being elusive. Using resonant inelastic x-ray scattering (RIXS), we investigate the magnetic excitations in infinite-layer PrNiO2 thin films grown on two different substrates, namely SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) enforcing different strain on the nickelates films. The magnon bandwidth of PrNiO2 shows only marginal response to strain-tuning, in sharp contrast to the enhancement of the superconducting transition temperature Tc in the doped superconducting samples. These results suggest the bandwidth of spin excitations of the parent compounds is similar under strain while Tc in the doped ones is not, and thus provide important empirics for the understanding of superconductivity in infinite-layer nickelates.

  View details for DOI 10.1038/s41467-024-49940-4

  View details for PubMedID 38956078

• Highly confined epsilon-near-zero and surface phonon polaritons in SrTiO3 membranes. Nature communications Xu, R., Crassee, I., Bechtel, H. A., Zhou, Y., Bercher, A., Korosec, L., Rischau, C. W., Teyssier, J., Crust, K. J., Lee, Y., Gilbert Corder, S. N., Li, J., Dionne, J. A., Hwang, H. Y., Kuzmenko, A. B., Liu, Y. 2024; 15 (1): 4743

  Abstract

  Recent theoretical studies have suggested that transition metal perovskite oxide membranes can enable surface phonon polaritons in the infrared range with low loss and much stronger subwavelength confinement than bulk crystals. Such modes, however, have not been experimentally observed so far. Here, using a combination of far-field Fourier-transform infrared (FTIR) spectroscopy and near-field synchrotron infrared nanospectroscopy (SINS) imaging, we study the phonon polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3 transferred on metallic and dielectric substrates. We observe a symmetric-antisymmetric mode splitting giving rise to epsilon-near-zero and Berreman modes as well as highly confined (by a factor of 10) propagating phonon polaritons, both of which result from the deep-subwavelength thickness of the membranes. Theoretical modeling based on the analytical finite-dipole model and numerical finite-difference methods fully corroborate the experimental results. Our work reveals the potential of oxide membranes as a promising platform for infrared photonics and polaritonics.

  View details for DOI 10.1038/s41467-024-47917-x

  View details for PubMedID 38834672

  View details for PubMedCentralID 9799068

• Coexistence of Interacting Charge Density Waves in a Layered Semiconductor. Physical review letters Lv, B. Q., Zong, A., Wu, D., Nie, Z., Su, Y., Choi, D., Ilyas, B., Fichera, B. T., Li, J., Baldini, E., Mogi, M., Huang, Y. B., Po, H. C., Meng, S., Wang, Y., Wang, N. L., Gedik, N. 2024; 132 (20): 206401

  Abstract

  Coexisting orders are key features of strongly correlated materials and underlie many intriguing phenomena from unconventional superconductivity to topological orders. Here, we report the coexistence of two interacting charge-density-wave (CDW) orders in EuTe_{4}, a layered crystal that has drawn considerable attention owing to its anomalous thermal hysteresis and a semiconducting CDW state despite the absence of perfect Fermi surface nesting. By accessing unoccupied conduction bands with time- and angle-resolved photoemission measurements, we find that monolayers and bilayers of Te in the unit cell host different CDWs that are associated with distinct energy gaps. The two gaps display dichotomous evolutions following photoexcitation, where the larger bilayer CDW gap exhibits less renormalization and faster recovery. Surprisingly, the CDW in the Te monolayer displays an additional momentum-dependent gap renormalization that cannot be captured by density-functional theory calculations. This phenomenon is attributed to interlayer interactions between the two CDW orders, which account for the semiconducting nature of the equilibrium state. Our findings not only offer microscopic insights into the correlated ground state of EuTe_{4} but also provide a general nonequilibrium approach to understand coexisting, layer-dependent orders in a complex system.

  View details for DOI 10.1103/PhysRevLett.132.206401

  View details for PubMedID 38829092

• Possible strain-induced enhancement of the superconducting onset transition temperature in infinite-layer nickelates COMMUNICATIONS PHYSICS Ren, X., Li, J., Chen, W., Gao, Q., Sanchez, J. J., Hales, J., Luo, H., Rodolakis, F., Mcchesney, J. L., Xiang, T., Hu, J., Comin, R., Wang, Y., Zhou, X., Zhu, Z. 2023; 6 (1)

  View details for DOI 10.1038/s42005-023-01464-x

  View details for Web of Science ID 001114809100001

• Discovery of charge order in a cuprate Mott insulator. Proceedings of the National Academy of Sciences of the United States of America Kang, M., Zhang, C. C., Schierle, E., McCoy, S., Li, J., Sutarto, R., Suter, A., Prokscha, T., Salman, Z., Weschke, E., Cybart, S., Wei, J. Y., Comin, R. 2023; 120 (30): e2302099120

  Abstract

  Copper oxide superconductors universally exhibit multiple forms of electronically ordered phases that break the native translational symmetry of the CuO2 planes. In underdoped cuprates with correlated metallic ground states, charge/spin stripes and incommensurate charge density waves (CDWs) have been experimentally observed over the years, while early theoretical studies also predicted the emergence of a Coulomb-frustrated 'charge crystal' phase in the very lightly doped, insulating limit of CuO2 planes. Here, we search for signatures of CDW order in very lightly hole-doped cuprates from the 123 family RBa2Cu3O7 - δ (RBCO; R: Y or rare earth), by using resonant X-ray scattering, electron transport, and muon spin rotation measurements to resolve the electronic and magnetic ground states fully. Specifically, Pr is used to substitute Y at the R-site to systematically suppress the superconductivity and access the extremely low hole-doping regime of the cuprate phase diagram without changing the oxygen stoichiometry. X-ray scattering data taken on Pr-doped YBCO thin films reveal an in-plane CDW order that follows the same linear evolution of wave vector versus hole concentration as oxygen-underdoped YBCO but extends all the way to the insulating and magnetically ordered Mott limit. Combined with the recent observation of charge crystal phase on an insulating surface of Bi2Sr2CaCu2O8 + z, our results in RBCO suggest that this electronic symmetry breaking is universally present in very lightly doped CuO2 planes. These findings bridge the gap between the Mott insulating state and the underdoped metallic state and underscore the prominent role that Coulomb-frustrated electronic phase separation plays among all cuprates.

  View details for DOI 10.1073/pnas.2302099120

  View details for PubMedID 37459539

• Extreme ultraviolet transient gratings: A tool for nanoscale photoacoustics PHOTOACOUSTICS Foglia, L., Mincigrucci, R., Maznev, A. A., Baldi, G., Capotondi, F., Caporaletti, F., Comin, R., De Angelis, D., Duncan, R. A., Fainozzi, D., Kurdi, G., Li, J., Martinelli, A., Masciovecchio, C., Monaco, G., Milloch, A., Nelson, K. A., Occhialini, C. A., Pancaldi, M., Pedersoli, E., Pelli-Cresi, J. S., Simoncig, A., Travasso, F., Wehinger, B., Zanatta, M., Bencivenga, F. 2023; 29: 100453

  Abstract

  Collective lattice dynamics determine essential aspects of condensed matter, such as elastic and thermal properties. These exhibit strong dependence on the length-scale, reflecting the marked wavevector dependence of lattice excitations. The extreme ultraviolet transient grating (EUV TG) approach has demonstrated the potential of accessing a wavevector range corresponding to the 10s of nm length-scale, representing a spatial scale of the highest relevance for fundamental physics and forefront technology, previously inaccessible by optical TG and other inelastic scattering methods. In this manuscript we report on the capabilities of this technique in the context of probing thermoelastic properties of matter, both in the bulk and at the surface, as well as discussing future developments and practical considerations.

  View details for DOI 10.1016/j.pacs.2023.100453

  View details for Web of Science ID 000925925600001

  View details for PubMedID 36718271

  View details for PubMedCentralID PMC9883289

• Ultrafast signatures of spin and orbital order in antiferromagnetic alpha-Sr2CrO4 COMMUNICATIONS PHYSICS Lee, M., Occhialini, C., Li, J., Zhu, Z., Sirica, N. S., Mix, L. T., Kim, S., Yarotski, D. A., Comin, R., Prasankumar, R. P. 2022; 5 (1)

  View details for DOI 10.1038/s42005-022-01110-y

  View details for Web of Science ID 000903596700001

• Carrier Doping Physics of Rare Earth Perovskite Nickelates RENiO3 FRONTIERS IN PHYSICS Li, J., Ramanathan, S., Comin, R. 2022; 10

  View details for DOI 10.3389/fphy.2022.834882

  View details for Web of Science ID 000761124600001

• First-principles calculation of oxygen vacancy effects on the magnetic properties of the perovskite SrNiO3 PHYSICAL REVIEW MATERIALS Cho, E., Klyukin, K., Ning, S., Li, J., Comin, R., Green, R. J., Yildiz, B., Ross, C. A. 2021; 5 (9)

  View details for DOI 10.1103/PhysRevMaterials.5.094413

  View details for Web of Science ID 000705563900004

• Doping-dependent phonon anomaly and charge-order phenomena in the HgBa2CuO4+delta and HgBa2CaCu2O6+delta superconductors PHYSICAL REVIEW B Wang, L., Yu, B., Jing, R., Luo, X., Zeng, J., Li, J., Bialo, I., Bluschke, M., Tang, Y., Freyermuth, J., Yu, G., Sutarto, R., He, F., Weschke, E., Tabis, W., Greven, M., Li, Y. 2020; 101 (22)

  View details for DOI 10.1103/PhysRevB.101.220509

  View details for Web of Science ID 000541410600001

• Temperature-independent thermal radiation PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Shahsafi, A., Roney, P., Zhou, Y., Zhang, Z., Xiao, Y., Wan, C., Wambold, R., Salman, J., Yu, Z., Li, J., Sadowski, J. T., Comin, R., Ramanathan, S., Kats, M. A. 2019; 116 (52): 26402-26406

  Abstract

  Thermal emission is the process by which all objects at nonzero temperatures emit light and is well described by the Planck, Kirchhoff, and Stefan-Boltzmann laws. For most solids, the thermally emitted power increases monotonically with temperature in a one-to-one relationship that enables applications such as infrared imaging and noncontact thermometry. Here, we demonstrated ultrathin thermal emitters that violate this one-to-one relationship via the use of samarium nickel oxide (SmNiO3), a strongly correlated quantum material that undergoes a fully reversible, temperature-driven solid-state phase transition. The smooth and hysteresis-free nature of this unique insulator-to-metal phase transition enabled us to engineer the temperature dependence of emissivity to precisely cancel out the intrinsic blackbody profile described by the Stefan-Boltzmann law, for both heating and cooling. Our design results in temperature-independent thermally emitted power within the long-wave atmospheric transparency window (wavelengths of 8 to 14 µm), across a broad temperature range of ∼30 °C, centered around ∼120 °C. The ability to decouple temperature and thermal emission opens a gateway for controlling the visibility of objects to infrared cameras and, more broadly, opportunities for quantum materials in controlling heat transfer.

  View details for DOI 10.1073/pnas.1911244116

  View details for Web of Science ID 000504656900041

  View details for PubMedID 31848248

  View details for PubMedCentralID PMC6936496

• Carrier localization in perovskite nickelates from oxygen vacancies PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Kotiuga, M., Zhang, Z., Li, J., Rodolakis, F., Zhou, H., Sutarto, R., He, F., Wang, Q., Sun, Y., Wang, Y., Aghamiri, N., Hancock, S., Rokhinson, L. P., Landau, D. P., Abate, Y., Freeland, J. W., Comin, R., Ramanathan, S., Rabe, K. M. 2019; 116 (44): 21992-21997

  Abstract

  Point defects, such as oxygen vacancies, control the physical properties of complex oxides, relevant in active areas of research from superconductivity to resistive memory to catalysis. In most oxide semiconductors, electrons that are associated with oxygen vacancies occupy the conduction band, leading to an increase in the electrical conductivity. Here we demonstrate, in contrast, that in the correlated-electron perovskite rare-earth nickelates, RNiO3 (R is a rare-earth element such as Sm or Nd), electrons associated with oxygen vacancies strongly localize, leading to a dramatic decrease in the electrical conductivity by several orders of magnitude. This unusual behavior is found to stem from the combination of crystal field splitting and filling-controlled Mott-Hubbard electron-electron correlations in the Ni 3d orbitals. Furthermore, we show the distribution of oxygen vacancies in NdNiO3 can be controlled via an electric field, leading to analog resistance switching behavior. This study demonstrates the potential of nickelates as testbeds to better understand emergent physics in oxide heterostructures as well as candidate systems in the emerging fields of artificial intelligence.

  View details for DOI 10.1073/pnas.1910490116

  View details for Web of Science ID 000493720200013

  View details for PubMedID 31611403

  View details for PubMedCentralID PMC6825322

• Putting the gap on the map NATURE PHYSICS Li, J., Comin, R. 2019; 15 (8): 736-738

  View details for DOI 10.1038/s41567-019-0513-9

  View details for Web of Science ID 000478082100014

• Resolving the nature of electronic excitations in resonant inelastic x-ray scattering PHYSICAL REVIEW B Kang, M., Pelliciari, J., Krockenberger, Y., Li, J., McNally, D. E., Paris, E., Liang, R., Hardy, W. N., Bonn, D. A., Yamamoto, H., Schmitt, T., Comin, R. 2019; 99 (4)

  View details for DOI 10.1103/PhysRevB.99.045105

  View details for Web of Science ID 000454767200008

• Growth and characterization of HgBa2CaCu2O6 +/-delta and HgBa2Ca2Cu3O8 +/-delta crystals PHYSICAL REVIEW MATERIALS Wang, L., Luo, X., Li, J., Zeng, J., Cheng, M., Freyermuth, J., Tang, Y., Yu, B., Yu, G., Greven, M., Li, Y. 2018; 2 (12)

  View details for DOI 10.1103/PhysRevMaterials.2.123401

  View details for Web of Science ID 000452685700001

• Perovskite nickelates as electric-field sensors in salt water NATURE Zhang, Z., Schwanz, D., Narayanan, B., Kotiuga, M., Dura, J. A., Cherukara, M., Zhou, H., Freeland, J. W., Li, J., Sutarto, R., He, F., Wu, C., Zhu, J., Sun, Y., Ramadoss, K., Nonnenmann, S. S., Yu, N., Comin, R., Rabe, K. M., Sankaranarayanan, S. S., Ramanathan, S. 2018; 553 (7686): 68-+

  Abstract

  Designing materials to function in harsh environments, such as conductive aqueous media, is a problem of broad interest to a range of technologies, including energy, ocean monitoring and biological applications. The main challenge is to retain the stability and morphology of the material as it interacts dynamically with the surrounding environment. Materials that respond to mild stimuli through collective phase transitions and amplify signals could open up new avenues for sensing. Here we present the discovery of an electric-field-driven, water-mediated reversible phase change in a perovskite-structured nickelate, SmNiO3. This prototypical strongly correlated quantum material is stable in salt water, does not corrode, and allows exchange of protons with the surrounding water at ambient temperature, with the concurrent modification in electrical resistance and optical properties being capable of multi-modal readout. Besides operating both as thermistors and pH sensors, devices made of this material can detect sub-volt electric potentials in salt water. We postulate that such devices could be used in oceanic environments for monitoring electrical signals from various maritime vessels and sea creatures.

  View details for DOI 10.1038/nature25008

  View details for Web of Science ID 000419769300031

  View details for PubMedID 29258293

• Habituation based synaptic plasticity and organismic learning in a quantum perovskite NATURE COMMUNICATIONS Zuo, F., Panda, P., Kotiuga, M., Li, J., Kang, M., Mazzoli, C., Zhou, H., Barbour, A., Wilkins, S., Narayanan, B., Cherukara, M., Zhang, Z., Sankaranarayanan, S. S., Comin, R., Rabe, K. M., Roy, K., Ramanathan, S. 2017; 8: 240

  Abstract

  A central characteristic of living beings is the ability to learn from and respond to their environment leading to habit formation and decision making. This behavior, known as habituation, is universal among all forms of life with a central nervous system, and is also observed in single-cell organisms that do not possess a brain. Here, we report the discovery of habituation-based plasticity utilizing a perovskite quantum system by dynamical modulation of electron localization. Microscopic mechanisms and pathways that enable this organismic collective charge-lattice interaction are elucidated by first-principles theory, synchrotron investigations, ab initio molecular dynamics simulations, and in situ environmental breathing studies. We implement a learning algorithm inspired by the conductance relaxation behavior of perovskites that naturally incorporates habituation, and demonstrate learning to forget: a key feature of animal and human brains. Incorporating this elementary skill in learning boosts the capability of neural computing in a sequential, dynamic environment.Habituation is a learning mechanism that enables control over forgetting and learning. Zuo, Panda et al., demonstrate adaptive synaptic plasticity in SmNiO3 perovskites to address catastrophic forgetting in a dynamic learning environment via hydrogen-induced electron localization.

  View details for DOI 10.1038/s41467-017-00248-6

  View details for Web of Science ID 000407552400001

  View details for PubMedID 28808316

  View details for PubMedCentralID PMC5556077

• Prominent Role of Spin-Orbit Coupling in FeSe Revealed by Inelastic Neutron Scattering PHYSICAL REVIEW X Ma, M., Bourges, P., Sidis, Y., Xu, Y., Li, S., Hu, B., Li, J., Wang, F., Li, Y. 2017; 7 (2)

  View details for DOI 10.1103/PhysRevX.7.021025

  View details for Web of Science ID 000401662800001

• Nematic Crossover in BaFe2As2 under Uniaxial Stress PHYSICAL REVIEW LETTERS Ren, X., Duan, L., Hu, Y., Li, J., Zhang, R., Luo, H., Dai, P., Li, Y. 2015; 115 (19): 197002

  Abstract

  Raman scattering can detect spontaneous point-group symmetry breaking without resorting to single-domain samples. Here, we use this technique to study BaFe(2)As(2), the parent compound of the "122" Fe-based superconductors. We show that an applied compression along the Fe-Fe direction, which is commonly used to produce untwinned orthorhombic samples, changes the structural phase transition at temperature T(s) into a crossover that spans a considerable temperature range above T(s). Even in crystals that are not subject to any applied force, a distribution of substantial residual stress remains, which may explain phenomena that are seemingly indicative of symmetry breaking above T(s). Our results are consistent with an onset of spontaneous nematicity only below T(s).

  View details for DOI 10.1103/PhysRevLett.115.197002

  View details for Web of Science ID 000364216600006

  View details for PubMedID 26588407