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, GiaWei 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/slaveboson 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 metalinsulator 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 meanfield theory Zhijie Fan, Cheng Chen, GiaWei 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 meanfield 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 metalinsulator transition. In particular, our QMD method can properly account for the incoherent electronic excitations in the vicinity of the MottHubbard transition. We perform extensive simulations on a liquid Hubbard model, which can be viewed as a minimum model for the metalinsulator transition in the fluid alkali metal, such as liquid Cesium and Rubidium. Our work opens a new avenue for multiscale dynamical simulations and modeling of strongly correlated electron systems. 
Wednesday, March 16, 2022 11:54AM  12:06PM 
N64.00003: On the role of longwavelength disorder near a continuous bandwidthtuned metalinsulator 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 bandwidthtuned 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 longwavelength disorder due to twistangle inhomogeneities cannot be ignored near the critical point. Building on the theory of a continuous metalinsulator transition at fixed filling in the clean limit, we study the effects of mesoscale 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 orbitalselective Mott phase stable against interorbital 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 orbitalselective 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 interorbital hopping? Here, we use the singlesite dynamical meanfield theory (DMFT) to show that, at zero temperature, the OSMP, involving the Mottinsulating state of one orbital, is unstable against interorbital hopping to another, metallic orbital. We provide a lower bound for the interorbital Kondo scale T^{K}_{inter}, stabilizing the metallic phase. Importantly, however, this scale can be extremely small, so that the physics at energies or temperatures far above T^{K}_{inter} is indistinguishable from a hypothetical OSMP with T^{K}_{inter}=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 slavespin 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 selfoscillation of the Mott insulator VO_{2}, 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 antiphase 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 metalinsulator domain walls around the Mott point Martha Y Villagran, Nikolaos Mitsakos, TsungHan Lee, Eduardo Miranda, John H Miller, Vladimir Dobrosavljevic Mott systems often undergo a firstorder metalinsulator 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 metalinsulator domain walls around the Mott point. Our study, carried out using dynamical meanfield 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 "spinliquid" Mott systems. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N64.00007: Phase Diagram of the SuSchriefferHeegerHubbard model on a square lattice Chunhan Feng, Bo Xing, Dario Poletti, Richard T Scalettar, George Batrouni The Hubbard and SuSchriefferHeeger Hamiltonians (SSH) are iconic models for understanding the qualitative effects of electronelectron and electronphonon interactions respectively. In the twodimensional square lattice Hubbard model at half filling, the onsite 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 electronphonon coupling λ is less than a critical value λ_{c} and a bond order wave when λ>λ_{c}. In this work, we perform numerical studies on the square lattice optical SuSchriefferHeegerHubbard 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 firstorder transition between an antiferromagnetic phase and a bondordered 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 atomicscale disorder in a doped spinorbit 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 atomicscale insight has been limited. We use spinpolarized scanning tunneling microscopy to image the evolution of spinresolved modulations originating from antiferromagnetic (AF) ordering in a spinorbit Mott insulator Sr_{3}Ir_{2}O_{7 }as a function of chemical composition and temperature. We find that replacing only several percent of La for Sr leads to nanometerscale AF puddles clustering away from La substitutions preferentially located in the middle SrO layer. Thermal erasure and reentry into the lowtemperature 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 atomicscale disorder in electron doped Sr_{3}Ir_{2}O_{7}. 
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 recently^{1} shown that this can be done starting from the HatsugaiKohmoto^{2} model which can be understood^{3} generally as the minimal model that breaks the nonlocal Z_{2} 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/T_{1} 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 T_{c} 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 T_{c}, 3) Mottness destroys the HebelSlichter peak in NMR, 4) The ultrasonic attenuation has a Mottinduced logarithmic suppression, and 5) Mottness changes the sign of the quartic coefficient in the LandauGinzburg freeenergy 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 lowtemperature properties of metals can be understood in terms of longlived quasiparticles with all complex interactions included in Fermiliquid 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 frequencyresolved probes that measure the complex optical conductivity σ_{1}(ω) + iσ_{2}(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 Fermiliquid behavior with T^{2} and ω^{2} dependences of the optical scattering rate γ(ω), along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the IoffeRegelMott limit ρ ≫ ρ_{IRM }is accompanied by a 'displaced Drude peak' in σ_{1}(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 Sr_{2}IrO_{4} Amirreza Ataei, Gael Grissonnanche, MarieEve Boulanger, Lu Chen, Etienne Lefrancois, Veronique Brouet, Louis Taillefer Strontium iridate, Sr_{2}IrO_{4}, is a spinorbitinduced Mott insulator that is isostructural to the cuprate La_{2}CuO_{4}, which is a chargetransfer Mott insulator. Various broken symmetries in the temperaturedoping 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: Ingap band in the onedimensional twoorbital KanamoriHubbard model with interorbital Coulomb interaction Nair S Aucar Boidi We study the electronic spectral properties at zero temperature of the onedimensional (1D) version of the degenerate twoorbital Kanamori Hubbard model (KHM) using stateoftheart numerical techniques based on the Density Matrix Renormalization Group. While the system is Mott insulating for the halffilled case we find interesting and rich structures in the singleparticle density of states (DOS) for the holedoped system. We find the existence of ingap states which are pulled down to lower energies from the upper Hubbard band (UHB) with increasing the interorbital 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 ingap excitations are formed mainly by interorbital holondoublon (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 ingap band, as expected from the twoparticle 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 multiorbital compounds. 
Wednesday, March 16, 2022 1:54PM  2:06PM Withdrawn 
N64.00013: Universal sizedependent nonlinear charge transport in single crystals of the Mott insulator Ca_{2}RuO_{4} 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 Ca_{2}RuO_{4} an attractive candidate material for developing Mottbased 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 highpurityCa_{2}RuO_{4} 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 Ca_{2}RuO_{4} out of the insulating state into a nonequilibrium 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 Ca_{2}RuO_{4} 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 metalinsulator 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 nonlinear change of screening of longrange 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 longrange Coulomb interaction and the strong onsite correlation, via an dynamical meanfield extension of density functional calculation. We found that in the relevant range of lattice spacing, the system is in the chargetransfer regime, namely the charge fluctuation involves mostly higher energy orbitals beyond 1s one, rendering a singleband 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 metalinsulator transition in realistic materials. 
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