Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P44: Mott PhysicsLive
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Sponsoring Units: DCMP Chair: Philip Phillips, University of Illinois at Urbana-Champaign |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P44.00001: Large light-induced modulation of the Metal Insulator Transition in photoconductor/Mott heterostructures Henry Navarro, Javier del Valle, Yoav Kalcheim, Nicolas M Vargas, Coline Adda, Minhan Lee, Pavel Lapa, Alberto Rivera, Ivan Zaluzhnyy, Erbin Qiu, Oleg Shpyrko, Marcelo Rozenberg, Alex Frano, Ivan Schuller Some Mott insulators exhibit a metal-to-insulator transition (MIT) across which the electrical resistance shows large changes. Modification of the electrical transport with an electric field has been extensively investigated and its use in emerging applications such as neuromorphic computing and voltage controlled optoelectronics seems very promising. Here we investigate the modification of the transport properties with light. We have discovered large effects using heterostructures consisting of a photoconductor CdS, film on top of ultrathin layers of the archetypal Mott insulators: VO2 or V2O3. For CdS/VO2, we observed a non-volatile light induced modulations of the MIT resulting in resistance changes of up to 3 orders of magnitude. On the other hand, for the CdS/V2O3 bilayer, we found a volatile light-induced modulations of the transition temperature (TMIT) of ~140 K, with resistance changes as large as 6 orders of magnitude. We will discuss the possible physical origin of this interesting effect. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P44.00002: Nano-scale ultrafast dynamics of Mott Insulating Ca2-xSrxRuO4 Rocco Vitalone, Aaron Sternbach, Ben Foutty, Alexander S McLeod, Chanchal Sow, Denis Golez, Fumihiko Nakamura, Yoshiteru Maeno, Abhay Narayan, Antoine Georges, Andrew Millis, Dmitri Basov Ca2RuO4 is a correlated transition metal oxide that exhibits a Mott transition (IMT) concurrent with a symmetry preserving Jahn-Teller distortion (JT) at 350 K. This strong coupling between the electronic and structural transitions in Ca2RuO4 makes studying the role played by individual degrees of freedom nontrivial. Since the Mott insulating state relies on a half-filled band, it is instructive to use optical photo-excitation to disrupt orbital ordering and the associated Mott State without directly perturbing the crystal structure. Using spectroscopic measurements with sub-picosecond temporal resolution and nano-scale spatial resolution, we interrogate the interplay and level of codependency of the JT and IMT via thermal cycling through the transition and electron-hole injection. Through the thermodynamic pathway, we observe phase coexistence in the form of a stripe phase existing at the domain wall between bulk insulating and metallic regions. Through the ultrafast carrier injection pathway, we observe the formation of localized mid-gap states that lead to enhanced absorption in the time domain with no spatial inhomogeneity. We posit that these mid-gap states become localized via polaronic features related to the local perturbation of the JT distortion. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P44.00003: Soft x-ray absorption study of the doped Mott insulator Y1-xCaxTiO3 Sajna Hameed, Joseph Joe, John Freeland, Martin Greven Metal-insulator transitions are ubiquitous in condensed matter physics and have been the subject of decades of extensive research. Rare-earth titanates are Mott-Hubbard insulators which exhibit such transitions into a metallic phase upon charge carrier doping. Depending on the rare-earth ion, the doping at which the transition occurs varies widely; La1-xSrxTiO3 requires as little as x = 0.05 to become metallic, whereas Y1-xCaxTiO3 turns metallic only at x = 0.4. YTiO3 is particularly interesting due to this enhanced stability of the insulating state against charge-carrier doping. We report a detailed X-ray absorption spectroscopic (XAS) study of the electronic structure across the insulator-metal transition in Y1-xCaxTiO3. From Ti L-edge XAS, we find that Ca-doping is associated with a proportional increase in the volume fraction of the Ti4+ content. O K-edge XAS reveals that the insulator-metal transition is driven by a formation of in-gap states of mixed O 2p and Ti 3d character, which increase in spectral intensity with increasing doping as well as decreasing temperature, eventually leading to the closing of the charge gap. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P44.00004: Pseudogap universality in the doping-driven metal to Mott-insulator transition Pierre-Olivier Downey, Nicolas KOWALSKI, Giovanni Sordi, Olivier Gingras, Charles-David Hebert, Maxime Charlebois, A.-M. S. Tremblay A pseudogap was observed in the doping-driven metal to Mott-insulator transition using Cluster Dynamical Mean-Field Theory (CDMFT) for the Hubbard model on small 2×2 square clusters1. Here, we show that this pseudogap displays some universal behavior under the change of temperature T, hopping terms t' and double occupancy cost U. We use three different approaches : the one band model for a 2×2 square cluster using CDMFT, the three band model for a 2×2 square cluster using CDMFT, and the one-band model for a 3×2 cluster using the Dynamical Cluster Approximation (DCA). We find that, if there is a first order transition, the filling as a function of shifted chemical potential μ does not depend on either U, T nor t' for t' in the interval [0.4,1]. The electron-doped and hole-doped cases however are different. Defining μPG as the chemical potential that we considered to be the beginning of the pseudogap phase (n=0.995), we also find that μPG does not vary with U as long as one is in the strong interaction regime. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P44.00005: Emergence of Competing Stripe Phase near the Mott Transition in Ti-doped Bilayer Calcium Ruthenates Ashish Gangshettiwar, Yanglin Zhu, Jin Peng, Yu Wang, Zhanzhi Jiang, Jiaming He, Jianshi Zhou, Zhiqiang Mao, Keji Lai The physics of nanoscale phase separation is at the heart of strongly correlated materials, where multiple degrees of freedom such as charge, spin, lattice, and orbital are simultaneously active. Using microwave impedance microscopy, we spatially resolved the coexisting phases on a Ca3(Ru0.9Ti0.1)2O7 bulk crystal during the metal-insulator transition. Different from a typical first- order phase transition where coexistence of the two terminal phases takes place, a new stripe phase oriented along the in-plane crystalline axes emerges inside both the G-type antiferromagnetic insulating state and paramagnetic metallic state. The effect of this electronic state can be observed in macroscopic measurements, allowing us to construct a phase diagram that takes into account the energetically competing phases. Our work provides a model approach to correlate macroscopic properties and mesoscopic phase separation in complex oxides. Furthermore, we investigate Ca3(Ru0.92Mn0.08)2O7 crystal to study the effect of magnetic dopants on the Metal-Insulator phase transition. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P44.00006: Ultrathin, rutile Mott insulator VO2 investigated by optical spectroscopy David Lahneman, Muhammad M Qazilbash, Douglas B. Beringer, Tetiana Slusar, Hyun-Tak Kim Transition metal oxides exhibit diverse emergent phenomena such as strongly correlated Mott insulating states, high-temperature superconductivity, magnetic and structural phase transitions, and metal-insulator transitions. Here, we focus on the thermally-driven metal-insulator transition (MIT) in vanadium dioxide (VO2). It is controversial whether the MIT in a thick VO2 film is accompanied by a simultaneous structural phase transition (SPT) or whether the MIT and SPT occur at different temperatures. The SPT is a Peierls ordering of all the vanadium atoms into dimerized pairs. Some theoretical proposals have been advanced to explain the MIT as a Peierls transition in which the SPT is assigned a crucial role. Here we report experiments on ultrathin VO2 film on rutile (001) TiO2. We demonstrate an insulating phase in ultrathin, rutile VO2 without Peierls ordering. The energy gap in rutile, insulating VO2 arises from electron-electron interactions, not from the pairing of vanadium atoms. Hence, the MIT studied in our work is a manifestation of a Mott transition. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P44.00007: Orbital magnetism in an electric field-driven Mott insulator Subrata Chakraborty, So Takei Motivated by the recent discovery of electric field-induced strong diamagnetism |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P44.00008: Spin orbital singlet formation and fluctuations in the Cluster Mott Insulator GaTa4Se8 Tsung-Han Yang, Tomoya Higo, Shinya Kawamoto, Satoru Nakatsuji, Kemp Plumb The magnetism in spin-orbit Mott insulators is closely related to the interplay between electronic correlations and spin-orbit couplings which often give rise to novel quantum phases of matter. In the Lacunar spinel GaTa4Se8, electronic correlations localize a single unpaired electron on tetrahedral clusters of Ta ions, while spin-orbit coupling generates Jeff=3/2 magnetic degrees of freedom. At T=50 K, GaTa4Se8 undergoes a magnetic transition accompanied by a structural dimerization. The magnetic ground states are entangled to the lattice distortion and a preceding phonon mode was observed by neutron scattering measurements. However, the mechanism of this preceding phonon mode is still unclear. In this presentation, I will present our crystallographic results following a series of neutron scattering measurements which provide more insights to the correlations between lattice and spin-orbital jeff=3/2 states in cluster spin-orbit Mott insulator. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P44.00009: Electrical conductivity of solid solutions between metal-like lead- and insulating yttrium ruthenate Sepideh Akhbarifar A metal-insulator transition (MIT) is observed when doping the strongly correlated electron system lead ruthenate pyrochlore with yttrium. Lead ruthenate (Pb2Ru2O6.5) has metal-like conductivity and is metallic Pauli paramagnetic, whereas yttrium ruthenate (Y2Ru2O7) is an antiferromagnetic mott insulator. In Pb2-xYxRu2O6.5+z solid solutions, x is increased from 0 to 2. The MIT occurs at x ≈ 0.2, which is mathematically analyzed in a new way and explained by the Mott–Hubbard mechanism of electron localization. Obviously, a critical content of yttrium is needed to open the Mott–Hubbard energy gap and to fill the lower Hubbard band (LHB) with localized electrons. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P44.00010: Quantum Molecular Dynamics Simulation with Dynamical Mean Field Theory Zhijie Fan, Gia-wei Chern We develop a novel scheme of adiabatic quantum molecular dynamics (QMD) in which the electron degrees of freedom are integrated out on the fly by the dynamical mean field theory (DMFT) calculation. Compared with the QMD based on the popular density functional theory, our new scheme is able to describe phenomena due to strong electron correlation such as Mott metal-insulator transition. Moreover, our DMFT-QMD also provides information on the incoherent non-qausi-particle electronic excitations, thus significantly generalizing the capability of Gutzwiller/Slave-boson based QMD recently developed by our group. We use this new MD method to study the Mott transition in an atomic liquid of hydrogen-like atoms. We observe a reentrant phase transition driven by Coulomb repulsion and obtain various nontrivial atomic and electronic properties of the system. Our work opens a new avenue for multi-scale dynamical simulations and modeling of strongly correlated electron systems. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P44.00011: Low-Temperature Dielectric Anomaly Arising from Electronic Phase Separation at the Mott Insulator-Metal Transition Yuting Tan, Andrej Pustogow, Roland Rösslhuber, Ece Uykur, Annette Böhme, Maxim Wenzel, Yohei Saito, Anja Löhle, Ralph Hübner, A. Kawamoto, John A Schlueter, Vladimir Dobrosavljevic, Martin Dressel Coulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T=0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε1 when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P44.00012: Theoretical study of nonlinear optical responses of non-centrosymmetric Mott insulators Hiroki Nishizawa, Sota Kitamura, Takahiro Morimoto Non-centrosymmetric materials host second-order nonlinear optical responses of electrons such as second harmonic generation and shift current. While formulation of these optical responses in non-interacting systems is well known and is actively studied, such formulation cannot be directly applied to systems with strong interaction effects. In this study, we investigate nonlinear optical responses in non-centrosymmetric Mott insulators, by studying the so called Rice-Mele model with Hubbard interaction by slave-rotor representation. We obtain its phase diagram and compute linear and nonlinear optical responses with a diagrammatic method. |
Wednesday, March 17, 2021 5:24PM - 5:36PM On Demand |
P44.00013: Volatile and non-volatile resistive switching in Mott materials Minhan Lee, Shaobo Cheng, Coline Adda, Javier del Valle, Yimei Zhu, Ivan Schuller Electrically-induced resistive switching offers new opportunities to emulate spiking neurons and plastic synapses for neuromorphic computing. Examples of materials exhibiting such behavior include several vanadium oxides, correlated nickelates, titanium dioxide, and many more. Manipulating the resistive switching properties of these oxides and modifying their transport properties are crucial for the development of future oxide electronics. In this work, we investigated the switching mechanisms behind volatile and non-volatile resistive switching in Mott materials, mainly focusing on vanadium oxides. The metal-insulator transition properties of the conductive filament and its nanoscale lattice structure will be discussed. Our study offers new insight into which mechanism dominates the switching process: electroforming or metal-insulator transition. |
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