Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N64: Mott PhysicsRecordings Available
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Sponsoring Units: DCMP Chair: Mahmoud Asmar, Kennesaw State University Room: Hyatt Regency Hotel -Grant Park B |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N64.00001: Phase diagrams of the Hubbard liquid model Chen Cheng, Gia-Wei Chern The Hubbard model is one of the most studied systems of strongly correlated electrons on the lattice. Here we propose a simple model system that generalizes the Hubbard model to an atomic liquid. Contrary to crystalline or amorphous solids where atoms are fixed, the motion of atoms in a liquid is strongly affected by the electronic structure, which in turn depends on the instantaneous ionic configuration. The Hubbard liquid model thus serves as a basic platform to investigate the nontrivial interplay between atomic dynamics and electronic correlation. Moreover, we show that the Hubbard liquid can also be viewed as a minimum model to describe the structural and electronic properties of fluid alkali metals, such as the liquid Cesium and Rubidium. We obtain the phase diagram of the Hubbard liquid model using a novel quantum molecular dynamics method in which the atomic forces are computed based on the Gutzwiller/slave-boson solution of a disordered Hubbard Hamiltonian. Characterizations of the three basic phases, the metallic cluster liquid, the dimerized insulator, and the Mott insulator, of the model are presented. We also discuss implications of our results to the metal-insulator transition in alkali liquids. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N64.00002: Atomistic simulation of Mott transition in liquid metal: Combining molecular dynamics with dynamical mean-field theory Zhijie Fan, Cheng Chen, Gia-Wei Chern Although extensive efforts have been devoted to understanding the effects of quenched disorder on correlated lattice models, much less is known about the Mott transition in an atomic liquid. Here 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. In particular, our QMD method can properly account for the incoherent electronic excitations in the vicinity of the Mott-Hubbard transition. We perform extensive simulations on a liquid Hubbard model, which can be viewed as a minimum model for the metal-insulator transition in the fluid alkali metal, such as liquid Cesium and Rubidium. Our work opens a new avenue for multi-scale dynamical simulations and modeling of strongly correlated electron systems. |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N64.00003: On the role of long-wavelength disorder near a continuous bandwidth-tuned metal-insulator transition Sunghoon Kim, Kin Fai Mak, Senthil Todadri, Debanjan Chowdhury Recent experiments in moiré transition metal dichalcogenide materials have reported the observation of a continuous bandwidth-tuned transition from a Fermi liquid metal to a paramagnetic Mott insulator at fixed filling of one electron per moiré unit cell. While interactions play a dominant role in driving the Mott transition and in the disappearance of the electronic Fermi surface, the effects of long-wavelength disorder due to twist-angle inhomogeneities cannot be ignored near the critical point. Building on the theory of a continuous metal-insulator transition at fixed filling in the clean limit, we study the effects of meso-scale inhomogeneities near the critical point on transport and related quantities using the framework of random resistor networks. The results will be placed in the context of recent and ongoing experiments. |
Wednesday, March 16, 2022 12:06PM - 12:18PM |
N64.00004: Is the orbital-selective Mott phase stable against inter-orbital hopping? Fabian B Kugler, Gabriel Kotliar Orbital differentiation, seen e.g. via distinct effective electron masses, is an important notion for strongly correlated materials. An extreme form of it is the orbital-selective Mott phase (OSMP). In model studies, the OSMP can be easily realized with orbitals that have different bandwidths or occupations and do not hybridize with each other. But is the OSMP stable against inter-orbital hopping? Here, we use the single-site dynamical mean-field theory (DMFT) to show that, at zero temperature, the OSMP, involving the Mott-insulating state of one orbital, is unstable against inter-orbital hopping to another, metallic orbital. We provide a lower bound for the inter-orbital Kondo scale TKinter, stabilizing the metallic phase. Importantly, however, this scale can be extremely small, so that the physics at energies or temperatures far above TKinter is indistinguishable from a hypothetical OSMP with TKinter=0. We present analytical arguments supported by numerical results using the numerical renormalization group as DMFT impurity solver. We also compare our findings with previous slave-spin studies. |
Wednesday, March 16, 2022 12:18PM - 12:30PM |
N64.00005: Unusual phenomena on capacitively coupled stochastic spiking oscillators Erbin Qiu, Pavel Salev, Henry Navarro, Coline Adda, Junjie Li, Minhan Lee, Yoav Kalcheim, Ivan K Schuller We take advantage of the threshold resistive switching and self-oscillation of the Mott insulator VO2, to implement stochastic spiking oscillators, which resemble jittering behavior of biological neurons. Interestingly, we observe that the intrinsic spiking stochasticity has a strong impact on capacitively coupled oscillators. A deterministic anti-phase synchronization can be achieved when two oscillators are coupled with a small capacitor. However, as the capacitive coupling strength increases, the deterministic alternating spiking gives way to stochastic spiking patterns in which an oscillator may have counterintuitive stochastic disruptive events. The stochastic disruptions of the alternating sequence of coupled spiking oscillators leads to a multimodal inter spike interval (ISI) distribution which resembles the multimodal spiking behavior in biological sensory neurons. This may have potential applications in Spiking Neural Networks and other computing related applications. Using the stochastic disruptive events of coupled spiking oscillators, we are able to demonstrate random number generation with potential for cryptographic applications. |
Wednesday, March 16, 2022 12:30PM - 12:42PM |
N64.00006: Unexpectedly thick metal-insulator domain walls around the Mott point Martha Y Villagran, Nikolaos Mitsakos, Tsung-Han Lee, Eduardo Miranda, John H Miller, Vladimir Dobrosavljevic Mott systems often undergo a first-order metal-insulator transition, with an associated phase coexistence region exhibiting inhomogeneities and local phase separation, at finite temperatures. They typically include "bubbles," or domains of the respective phases, separated by surprisingly thick domain walls, as revealed both by imaging experiments and recent theoretical modeling. To further elucidate this unexpected behavior, we have performed a systematic model study of the structure of such metal-insulator domain walls around the Mott point. Our study, carried out using dynamical mean-field theory, reveals that a mechanism producing such thick domain walls can be traced to strong magnetic frustration. This behavior is expected to be a robust feature of "spin-liquid" Mott systems. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N64.00007: Phase Diagram of the Su-Schrieffer-Heeger-Hubbard model on a square lattice Chunhan Feng, Bo Xing, Dario Poletti, Richard T Scalettar, George Batrouni The Hubbard and Su-Schrieffer-Heeger Hamiltonians (SSH) are iconic models for understanding the qualitative effects of electron-electron and electron-phonon interactions respectively. In the two-dimensional square lattice Hubbard model at half filling, the on-site Coulomb repulsion, U, between up and down electrons induces antiferromagnetic (AF) order and a Mott insulating phase. On the other hand, for the SSH model, there is an AF phase when the electron-phonon coupling λ is less than a critical value λc and a bond order wave when λ>λc. In this work, we perform numerical studies on the square lattice optical Su-Schrieffer-Heeger-Hubbard Hamiltonian (SSHH), which combines both interactions. We use the determinant quantum Monte Carlo (DQMC) method which does not suffer from the fermionic sign problem at half filling. We map out the phase diagram and find that it exhibits a direct first-order transition between an antiferromagnetic phase and a bond-ordered wave as λ increases. The AF phase is characterized by two different regions. At smaller λ the behavior is similar to that of the pure Hubbard model; the other region, while maintaining long range AF order, exhibits larger kinetic energies and double occupancy, i.e. larger quantum fluctuations, similar to the AF phase found in the pure SSH model. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N64.00008: Imaging antiferromagnetic domain fluctuations and the effect of atomic-scale disorder in a doped spin-orbit Mott insulator Ilija Zeljkovic, He Zhao, Zachary Porter, Xiang Chen, Stephen D Wilson, Ziqiang Wang Correlated oxides can exhibit complex electronic and magnetic patterns. Understanding how magnetic domains form has been of great interest, but atomic-scale insight has been limited. We use spin-polarized scanning tunneling microscopy to image the evolution of spin-resolved modulations originating from antiferromagnetic (AF) ordering in a spin-orbit Mott insulator Sr3Ir2O7 as a function of chemical composition and temperature. We find that replacing only several percent of La for Sr leads to nanometer-scale AF puddles clustering away from La substitutions preferentially located in the middle SrO layer. Thermal erasure and re-entry into the low-temperature ground state leads to a spatial reorganization of the AF puddles. Our experiments reveal multiple stable AF domain configurations at low temperature, and shed light onto spatial fluctuations of the AF order around atomic-scale disorder in electron doped Sr3Ir2O7. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N64.00009: Thermodynamics of Superconductivity in a Doped Mott Insulator Jinchao Zhao, Philip W Phillips, Edwin Huang, Luke Yeo Being able to compute the superconducting properties starting from a computable model for a doped Mott insulator stands as a grand challenge. We have recently1 shown that this can be done starting from the Hatsugai-Kohmoto2 model which can be understood3 generally as the minimal model that breaks the non-local Z2 symmetry of a Fermi liquid, thereby constituting a new quartic fixed point for Mott physics. In the current work, we go beyond the previous T=0 analysis and compute the thermodynamics, condensation energy, and electronic properties such as the NMR relaxation rate 1/T1 and ultrasonic attenuation rate. Key differences arise from the BCS analysis from a Fermi liquid: 1) The pairing gap turns on at a temperature that exceeds Tc defined as the temperature at which the pair susceptibility (computable exactly) diverges, 2) The condensation energy exceeds that in BCS theory suggesting that, multiple Mott bands might be a way of enhancing Tc, 3) Mottness destroys the Hebel-Slichter peak in NMR, 4) The ultrasonic attenuation has a Mott-induced logarithmic suppression, and 5) Mottness changes the sign of the quartic coefficient in the Landau-Ginzburg free-energy fuctional relative to that in BCS. As all of these properties are observed in the cuprates, our analysis here points a way forward in computing superconducting properties of strongly correlated electron matter. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N64.00010: Rise and Fall of Landau's Quasiparticles While Approaching the Mott Transition Andrej Pustogow, Yohei Saito, Anja Löhle, Miriam Sanz Alonso, Atsushi Kawamoto, Vladimir Dobrosavljevic, Martin Dressel, Simone Fratini Landau suggested that the low-temperature properties of metals can be understood in terms of long-lived quasiparticles with all complex interactions included in Fermi-liquid parameters, such as the effective mass m*. Despite its wide applicability, electronic transport in bad or strange metals and unconventional superconductors is controversially discussed towards a possible collapse of the quasiparticle concept. Crucial information can be obtained by frequency-resolved probes that measure the complex optical conductivity σ1(ω) + iσ2(ω). Here we explore the electrodynamic response of correlated metals at half filling upon approaching a Mott insulator. The correlation strength U/W is varied by partial chemical substitution. We reveal persistent Fermi-liquid behavior with T2 and ω2 dependences of the optical scattering rate γ(ω), along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe-Regel-Mott limit ρ ≫ ρIRM is accompanied by a 'displaced Drude peak' in σ1(ω). Our results, supported by a theoretical model for the optical response, demonstrate the emergence of a bad metal from resilient quasiparticles that are subject to dynamical localization and dissolve near the Mott transition. |
Wednesday, March 16, 2022 1:30PM - 1:42PM |
N64.00011: Thermal Hall effect in Sr2IrO4 Amirreza Ataei, Gael Grissonnanche, Marie-Eve Boulanger, Lu Chen, Etienne Lefrancois, Veronique Brouet, Louis Taillefer Strontium iridate, Sr2IrO4, is a spin-orbit-induced Mott insulator that is isostructural to the cuprate La2CuO4, which is a charge-transfer Mott insulator. Various broken symmetries in the temperature-doping phase diagram of iridates point to similarities with the pseudogap phase of the cuprate superconductors [1]. |
Wednesday, March 16, 2022 1:42PM - 1:54PM |
N64.00012: In-gap band in the one-dimensional two-orbital Kanamori-Hubbard model with inter-orbital Coulomb interaction Nair S Aucar Boidi We study the electronic spectral properties at zero temperature of the one-dimensional (1D) version of the degenerate two-orbital Kanamori Hubbard model (KHM) using state-of-the-art numerical techniques based on the Density Matrix Renormalization Group. While the system is Mott insulating for the half-filled case we find interesting and rich structures in the single-particle density of states (DOS) for the hole-doped system. We find the existence of in-gap states which are pulled down to lower energies from the upper Hubbard band (UHB) with increasing the inter-orbital Coulomb interaction V. We analyze the composition of the DOS by projecting it onto different local excitations and we observe that for large dopings these in-gap excitations are formed mainly by inter-orbital holon-doublon (HD) states and their energies follow approximately the HD states in the atomic limit. We observe that the Hund interaction J increases the width of the in-gap band, as expected from the two-particle fluctuations in the Hamiltonian. The observation of a finite density of states within the gap between the Hubbard bands for this extended 1D model indicates that these systems present a rich excitation spectra which could help us understand the microscopic physics behind multi-orbital compounds. |
Wednesday, March 16, 2022 1:54PM - 2:06PM Withdrawn |
N64.00013: Universal size-dependent nonlinear charge transport in single crystals of the Mott insulator Ca2RuO4 Remko Fermin, Guerino Avallone, Kaveh Lahabi, Veronica Granata, Rosalba Fittipaldi, Carla Cirillo, Carmine Attanasio, Antonio Vecchione, Jan Aarts The surprisingly low current density required for inducing the insulator to metal transition has made Ca2RuO4 an attractive candidate material for developing Mott-based electronics devices. The mechanism driving the resistive switching, however, remains a controversial topic in the field of correlated electron systems. Here we probe an uncovered region of phase space by studying high-purityCa2RuO4 single crystals, using the sample size as principal tuning parameter. Upon reducing the crystal size, we find a four orders of magnitude increase in the current density required for driving Ca2RuO4 out of the insulating state into a non-equilibrium phase which is the precursor to the fully metallic phase. By integrating a microscopic platinum thermometer and performing thermal simulations, we gain insight into the local temperature during simultaneous application of current and establish that the size dependence is not a result of Joule heating. The findings suggest an inhomogeneous current distribution in the nominally homogeneous crystal. Our study calls for a reexamination of the interplay between sample size, charge current, and temperature in driving Ca2RuO4 towards the Mott insulator to metal transition. |
Wednesday, March 16, 2022 2:06PM - 2:18PM Withdrawn |
N64.00014: Nature of Mott transition in a hydrogen lattice Zijian Lang, Henry Tsang, Sudeshna Sen, Kristjan Haule, Vladimir Dobrosavljevic, Wei Ku Mott transition, an electron correlation induced metal-insulator transition, has long been realized in many materials. Yet, the microscopic nature of the transition proposed by Mott has not been carefully examined in these materials, even by modern theories. This is because Mott's original proposal makes use of non-linear change of screening of long-range Coulomb interaction that are almost always ignored in simple models used in previous study of Mott transition. Here we study the Mott transition of an artificial hydrogen lattice including both the long-range Coulomb interaction and the strong on-site correlation, via an dynamical mean-field extension of density functional calculation. We found that in the relevant range of lattice spacing, the system is in the charge-transfer regime, namely the charge fluctuation involves mostly higher energy orbitals beyond 1s one, rendering a single-band Hubbard model inadequate. Interestingly, Mott transition occurs when atomic bound states are still present. Our study challenges Mott's original microscopic picture and reveal some key physics of metal-insulator transition in realistic materials. |
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