Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A43: Strange Metals and Novel Transport PropertiesLive

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Sponsoring Units: DCMP Chair: Tarapada Sarkar, University of Maryland, College Park 
Monday, March 15, 2021 8:00AM  8:12AM Live 
A43.00001: Measurement of the Planckian scattering rate Gael Grissonnanche, Yawen Fang, Anaelle Legros, Simon Verret, Francis Laliberte, Clement Collignon, Amirreza Ataei, Maxime Dion, Jianshi Zhou, David E Graf, Michael Lawler, Paul Goddard, Louis Taillefer, Brad Ramshaw Perfectly Tlinear resistivity is observed in a variety of strongly correlated metals close to a quantum critical point [1] and has been attributed to a scattering rate 1/τ of charge carriers that reaches the Planckian limit [2,3], with hbar/τ = α k_{B}T where α is of order unity. While this relationship is often inferred from simple estimates, a Tlinear scattering rate has yet to be measured. 
Monday, March 15, 2021 8:12AM  8:24AM Live 
A43.00002: Strange metal solution of the Hubbard model Aaram J. Kim, Philipp Werner, Evgeny Kozik The numerically exact boldline diagrammatic theory for the 2d Hubbard model exhibits a nonFermiliquid (NFL) strange metal state, which is connected to the SYK NFL in the stronginteraction limit. The solution for the doped system features the expected phenomenology with the NFL regime near half filling at strong couplings and in a wide temperature range enclosed by the atomic state at high temperatures and a Fermi liquid at low temperatures. However, the singularity structure of the diagrammatic series reveals that the solution in the halffilled and weakly doped regime corresponds to the unphysical branch of the LuttingerWard functional. On the other hand, our analysis suggests that in the optimally doped regime the characteristic NFL physics can be realized. 
Monday, March 15, 2021 8:24AM  8:36AM Live 
A43.00003: Strange semimetal dynamics in SrIrO3 Kaushik Sen, Dirk Fuchs, Rolf Heid, Kai Kleindienst, Karsten Wolff, Joerg Schmalian, Matthieu Le Tacon The interplay of electronic correlations, multiorbital excitations, and spinorbit coupling is a fertile ground for new states of matter in quantum materials. Here, we report on a polarized Raman scattering study of semimetallic SrIrO3. The momentumspace selectivity of Raman scattering allows to circumvent the challenge to resolve the dynamics of charges with very different mobilities. The Raman responses of both holes and electrons display an electronic continuum extending far beyond the energies allowed in a regular Fermi liquid. Analyzing this response within a memory function formalism, we extract their frequency dependent scattering rate and mass enhancement, from which we determine their DCmobilities and electrical resistivities that agree well with transport measurement. We demonstrate that its charge dynamics is well described by a marginal Fermi liquid phenomenology, with a scattering rate close to the Planckian limit. This demonstrates the potential of this approach to investigate the charge dynamics in multiband systems. 
Monday, March 15, 2021 8:36AM  8:48AM Live 
A43.00004: Firstprinciples calculation of the Hall coefficient using the Ong construction Sebastian ReyesLillo, Francisco Muñoz, Matthew Brahlek The Hall coefficient in the weak magnetic field semiclassical limit can be obtained using the geometrical construction of N. P. Ong (Phys. Rev. B 43, 193, 1991) in terms of the Stokes area swept out by the scattering path length vector on moving around the Fermi surface perimeter. We implement Ong’s relationship within the Pyprocar software suite (Comput. Phys. Commun. 251, 107080, 2020) and use firstprinciples calculations to compute the Hall coefficient for several complex oxide systems. For SrVO3, a prototypical strongly correlated system with a simple perovskite structure and isolated delectron bands, we compute the Hall coefficient along the [001] crystallographic direction and find good agreement with transport measurements in the hightemperature isotropic scatteringtime limit. We discuss extensions of the method to other strongly correlated materials with magnetic ordering and spinorbit interaction. 
Monday, March 15, 2021 8:48AM  9:00AM Live 
A43.00005: Revealing a large temperature dependence of the Hall effect in the “nonmetallic” metal FeCrAs Benny Lau, Wenlong Wu, Stephen R Julian The system FeCrAs presents a curious duality in its behaviour: its resistivity is in the metallic range, but with a nonmetallic temperature dependence from above 800 K to below 100 mK. Furthermore, a distorted Kagomé lattice magnetically frustrates Cr moments, which causes magnetic fluctuations that survive far beyond the antiferromagnetic ordering temperature of T_{N} ~ 125 K. Considering the strong anomaly in resistivity at T_{N}, along with a nonmetallic temperature dependence extending beyond 800 K, it is natural to postulate that the exotic scattering of electrons is closely tied to its magnetic fluctuations. 
Monday, March 15, 2021 9:00AM  9:12AM Live 
A43.00006: Exciton condensation in incoherent semimetals. Geo Jose, Bruno Uchoa We address the formation of exciton condensation in two coupled wires with incoherent fermions. Each wire is described by a twoband dispersive SYK model at half filling with quadratic dispersion and infinite band width. In the normal state, the model has near conformal symmetry and describes an incoherent semimetal with sublinear T^{2/5} temperature dependence of the resistivity. We show that the formation of indirect exciton condensation between the two wires can be solved exactly in the large N limit. We find that the condensation temperature scales as U^{5}, with U the strength of the repulsive coupling between the two wires. 
Monday, March 15, 2021 9:12AM  9:24AM Live 
A43.00007: Diamagneticlike response from localized heating of a paramagnetic material Yoshiteru Maeno, Giordano Mattoni, Shingo Yonezawa In the study of material properties outofequilibrium, the nonequilibrium steady states (NESS) induced by electric current are an appealing research direction where unconventional states may emerge. Especially, the effects of steady electric current on metalinsulator transitions and magnetic transitions in stronglycorrelated systems are attracting recent interests. However, the unavoidable Joule heating caused by flowing current calls for the development of new measurement protocols, with particular attention to the physical properties of the background materials involved. Here, we demonstrate that localized heating can give rise to a large, spurious diamagneticlike signal [1]. This occurs due to the local reduction of the background magnetization caused by the heated sample, provided the background material has a Curielike susceptibility. Our experimental results, along with numerical calculations, constitute an important building block for performing accurate magnetic measurements under the flow of electric current. 
Monday, March 15, 2021 9:24AM  9:36AM Live 
A43.00008: Bond stretching branch dispersions in undoped La_{2}CuO_{4} calculated using LDA+U Tyler Sterling, Aaron M Holder, Dmitry Reznik In undoped, insulating La_{2}CuO_{4} (LCO), the longitudinal CuO bondstretching branches are observed to be nearly dispersionless. As doping increases, these branches soften away from the zone center and disperse downwards towards the zone boundary. LDA calculations, which predict the undoped cuprates to be metallic, do not find the nearly dispersionless character of these modes. In the LDA, these branches disperse downward towards the zone boundary as in overdoped metallic LCO. In this work, we employ the HubbardU correction in the LDA+U method to calculate the dispersions for a range of U values. With U=6 eV, we find the insulating, antiferromagnetic ground state of LCO. Our calculations predict the bondstretching modes to be nearly dispersionless in the insulating ground state in agreement with experiment. 
Monday, March 15, 2021 9:36AM  9:48AM Live 
A43.00009: Linear in temperature resistivity and the manybody Kubo formula Hitesh Changlani, Aavishkar Patel The description of dynamics of strongly correlated quantum matter is a challenge, particularly in situations where a quasiparticle description is absent. In such situations, however, the manybody Kubo formula from linear response theory still remains valid. We address the puzzle of linear in temperature (Tlinear) resistivity seen in nonFermi liquid phases that occur in several condensed matter systems. We derive a simple criterion for the occurence of Tlinear resistivity based on an analysis of the contributions to the manybody Kubo formula, determined by an invariant “ffunction" involving current matrix elements and energy eigenvalues that describes the DC conductivity of the system in the microcanonical ensemble. Using full diagonalization, we test this criterion for the ffunction in several different models  the spinful Fermi Hubbard model and the spinless nearest neighbor Hubbard model, and in lattices of SachdevYeKitaev models with single particle hopping. We also discuss a shiftinvert algorithm to compute the ffunction on lattice sizes where Krylov techniques can be applied. 
Monday, March 15, 2021 9:48AM  10:00AM Live 
A43.00010: Bad metallic transport in geometrically frustrated models Juan MendezValderrama, Debanjan Chowdhury Numerous strongly correlated metals display nonFermi liquid (NFL) properties over a broad range of temperatures. The intermediatescale NFL often displays a regime of Tlinear resistivity, accompanied by a finite extrapolated zero temperature entropy. In this work, we study a family of geometrically frustrated models with an interaction scale far exceeding the singleparticle bandwidth. Starting from the interactiononly limit, which can be solved exactly, we study the transport and thermodynamic properties perturbatively at leading order in the singleparticle bandwidth. Over a broad range of intermediate temperatures, we find evidence of "bad" metallic behavior accompanied by Tlinear resistivity. At commensurate fillings, the badmetallic regime eventually crosses over into correlated insulators in the limit of low temperatures. We discuss the relevance of our results to experiments in coldatom and moiré heterostructure based platforms. 
Monday, March 15, 2021 10:00AM  10:12AM 
A43.00011: Electron Jamming and the Unusual Charge Response of Strange Metals Debanjan Chowdhury, Danilo Liarte, James Patarasp Sethna, Stephen Thornton Recent measurements [1] of the dynamical charge response of optimally doped cuprate “strange” metals have revealed a broad, featureless continuum of excitations, extending over much of the Brillouin zone. The nature of this continuum and the absence of a longlived plasmon excitation is strikingly at odds with the expectations of Fermi liquid theory. In this work, we investigate the bosonic collective modes and the particlehole excitations of strange metals by making an analogy to lattices falling apart across a “jamming” transition [2]. We reproduce many of the qualitative features of the measured densitydensity response of strange metals using the above framework and speculate on the possibility that strongly interacting electrons can undergo a jamming transition. 
Monday, March 15, 2021 10:12AM  10:24AM Live 
A43.00012: Hydrodynamic electron transport near charge neutrality Songci Li, Alex Levchenko, Anton Andreev We develop theory of hydrodynamic electron transport in a longrange disorder potential for conductors in which the underlying electron liquid lacks Galilean invariance. For weak disorder we express the transport coefficients in terms of the intrinsic kinetic coefficients of the electron liquid and the correlation function of the disorder potential. We apply these results to analyze the doping and temperaturedependence of transport coefficients of graphene devices. We show that at charge neutrality long range disorder increases the conductivity of the system above the intrinsic value, due to the predominantly vortical flow caused by local deviations from charge neutrality. Its magnitude is inversely proportional to the shear viscosity of the electron liquid and scales as the square of the disorder correlation radius. This is qualitatively different from the situation away from charge neutrality. In that case the flow is predominantly potential, and produces negative viscous contributions to the conductivity. 
Monday, March 15, 2021 10:24AM  10:36AM 
A43.00013: The Lorenz ratio of an impure compensated metal at intermediate temperatures WooRam Lee, Karen Michaeli, Georg Schwiete Recent experiments observed small Lorenz ratios in the compensated metal WP2, indicating that charge flow is strongly favored over heat conduction. Motivated by these findings, we study transport properties of compensated metals in the presence of electronelectron collisions and electronimpurity scattering. We focus on intermediate temperatures, where the phonon contributions to transport are weak and elastic and inelastic scattering rates are comparable. Our exact solution for the kinetic equation in the presence of general Fermiliquid interactions is used to extract the Lorenz ratio for short and long range interactions. We find that the Lorenz ratio develops a temperature dependence as well as gets enhanced as a consequence of disorder scattering. For collisions mediated by the Coulomb interaction, impurities give rise to a nonmonotonic dependence of the Lorenz ratio on the screening wave number. To help future experimental efforts, we establish a scheme to connect the exact results with the solution of the Boltzmann equation under the relaxation time approximation for all collision integrals, providing simple phenomenological expressions for the transport coefficients. 
Monday, March 15, 2021 10:36AM  10:48AM Live 
A43.00014: Monte Carlo Simulations of nonlinear evolution of materials resistivity Steven Hancock, David P Landau, Yohannes Abate We developed an experimentally motivated Monte Carlo simulation to calculate the conductance materials and the effect of charged dopant concentration and applied this method to investigate the nonlinear evolution of the resistivity with annealing time in oxygen deficient thin films. The model consists of an N x N square lattice with hydrogenic atoms placed at each lattice site. The valence electrons are bound to their respective lattice site via a harmonic potential, and electrons at different sites are allowed to interact via a screened Coulomb potential. At each Monte Carlo step, electrons attempt to slightly change their position with respect to their lattice site. Additionally, electrons attempt to transition between conducting and nonconducting states. We found nonlinear dependence of the resistance as a function of dopant concentration. The dopants act as electron traps where they lower the energy of nearby electrons and increase the energy requirement to transition to the conducting state. As more dopants are added, this effect increases, further suppressing the conductivity. This would indicate that the inclusion of the charged dopants advances the percolative evolution of such a phase transition. 
Monday, March 15, 2021 10:48AM  11:00AM 
A43.00015: Quasiparticle and NonQuasiparticle Transport in Doped Quantum Paraelectrics Abhishek Kumar, Vladimir I Yudson, Dmitrii Maslov Charge transport in doped quantum paralectrics (QPs) presents a number of puzzles, including a pronounced T^{2} regime in the resistivity. We analyze charge transport in a QP within a model of electrons coupled to a soft transverse optical (TO) mode via a twophonon mechanism. For T above the softmode frequency but below some characteristic scale (E_{0}), the resistivity scales with the occupation number of phonons squared, i.e., as T^{2}. The T^{2} scattering rate does not depend on the carrier number density and is not affected by a crossover between degenerate and nondegenerate regimes, in agreement with the experiment. Temperatures higher than E_{0} correspond to a nonquasiparticle regime, which we analyze by mapping the Dyson equation onto a problem of supersymmetric quantum mechanics. The combination of scattering by two TO phonons and by a longitudinal optical mode explains the data quite well. 
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