Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A06: Beyond Fermi Liquid TheoryFocus

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Sponsoring Units: DCMP Chair: Peter Riseborough, Temple University Room: BCEC 109A 
Monday, March 4, 2019 8:00AM  8:12AM 
A06.00001: Superdiffusive transport of energy in generic Luttinger liquids Joel Moore, Vir Bulchandani, Christoph Karrasch Metals in one spatial dimension are described at the lowest energy scales by the Luttinger liquid theory. It is well understood that this free theory, and even interacting integrable models, can support ballistic transport of conserved quantities including energy. Realistic Luttinger liquids, even in pure systems without disorder, contain integrabilitybreaking interactions, which are expected to lead to thermalization and conventional diffusive linear response. We show that the expansion of energy when such a nonintegrable Luttinger liquid is locally heated above its ground state shows superdiffusive behavior (i.e., spreading of energy that is intermediate between diffusion and ballistic propagation), by combining an analytical anomalous diffusion model with numerical matrix product state calculations. The main ingredient in the analytical model is the powerlaw in linearresponse transport that originates in the scaling dimension of integrabilitybreaking corrections to the Luttinger liquid. Some other onedimensional systems that also remain far from the linearresponse regime for long times are discussed. 
Monday, March 4, 2019 8:12AM  8:24AM 
A06.00002: Lorentz ratio of a compensated metal Songci Li, Dmitrii Maslov A violation of the WiedemannFranz law in a metal can quantified by comparing the Lorentz ratio, L=κρ/T, where κ is the thermal conductivity and ρ is the electrical resistivity, with the universal Sommerfeld constant, L_{0}=π^{2}/3) (k_{B}/e)^{2}. 
Monday, March 4, 2019 8:24AM  8:36AM 
A06.00003: Uncovering nonFermiliquid behavior in Hund metals: critical behavior of a threeorbital Kondo model Elias Walter, Katharina M Stadler, SeungSup B. Lee, Yilin Wang, Gabriel Kotliar, Andreas Weichselbaum, Jan Von Delft When using dynamical mean field theory (DMFT) to study Hund metals, one arrives at selfconsistent impurity models in which bath and impurity both have spin and orbital degrees of freedom. If these are screened at different energy scales, T_{K}^{sp} < T_{K}^{orb}, the intermediate energy window is governed by a novel nonFermiliquid (NFL) fixed point, involving screened orbital degrees of freedom weakly coupled to an unscreened local spin. Here we characterize the corresponding NFL behavior in detail for a 3orbital Kondo model, tuned such that the NFL energy window is very wide. We find excellent agreement between conformal field theory (CFT) predictions and numerical renormalization group (NRG) results. 
Monday, March 4, 2019 8:36AM  8:48AM 
A06.00004: Transport properties of a disordered twodimensional metal in the vicinity of SDW order: A memory matrix calculation Hermann Freire We perform the calculation of many transport coefficients as a function of temperature in the “strangemetal” phase that emerges in the vicinity of a SDW phase transition in the presence of weak disorder. This scenario is relevant to the phenomenology of many important correlated materials, such as, e.g., the cuprates and the ironbased superconductors. We implement the memorymatrix approach that allows the calculation of all transport coefficients for the corresponding fieldtheory model beyond the quasiparticle paradigm. As a result, we are able to obtain here the temperature dependence of the dc resistivity, the Hall angle, the thermal conductivity, the Seebeck coefficient and the Nernst response for a disordered twodimensional SDW quantum critical theory with an effective composite operator that couples the orderparameter fluctuations to the entire Fermi surface of the system. We argue that our present theory provides a good basis in order to unify the experimental transport data, e.g., of the cuprates, within a wide range of doping regimes. 
Monday, March 4, 2019 8:48AM  9:00AM 
A06.00005: Transconducting Transition for a Dynamic Boundary Coupled to Several TomonagaLuttinger Liquids Baruch Horovitz, Thierry Giamarchi, Pierre Le Doussal The question on how a quantum bath can affect the dynamical properties of a quantum degree of freedom is a long standing and important one. 
Monday, March 4, 2019 9:00AM  9:12AM 
A06.00006: Tlinear resistivity in models with local selfenergy EunAh Kim, Peter Cha, Aavishkar Patel, Emanuel C Gull Bad metallic transport is commonly observed in strongly correlated systems. In particular, Tlinear resistivity is of special theoretical interest in its connection to quantum criticality and superconductivity. Recently, Tlinear resistivity have been explicitly found in several models with local selfenergy yet relation between different mechanisms remain unclear. In this work, we discuss two models that demonstrate Tlinearity: latticeSachdevYeKitaev model and the Hubbard model within the dynamical meanfield theory (DMFT). In the former, we find that Tscaling depends crucially on the details of both the infrared and ultravioletlimits. In the latter, we study the Hubbard model within singlesite DMFT, and show that transport quantities and compressibility are driven by atomic interactions down to temperatures of the order of the bandwidth. We also study the temperature dependence of the Lorentz ratio and Diffusivity and contrast different mechanisms of Tlinear resistivity. 
Monday, March 4, 2019 9:12AM  9:24AM 
A06.00007: Theory of Strange Metals from Hot Fermions Connie Mousatov, Erez Berg, Sean Hartnoll We study a metal where a large Fermi surface coexists with a set of `hot spots' with a high density of states. The hot electrons occupy a small fraction of the Brillouin zone, yet qualitatively modify the properties of the entire system. We emphasize the importance of scattering processes in which two electrons from the large, `cold' Fermi surface scatter into one hot and one cold electron. These lead to 
Monday, March 4, 2019 9:24AM  9:36AM 
A06.00008: Emergent Anisotropic NonFermi Liquid SangEun Han, Changhee Lee, EunGook Moon, Hongki Min Understanding correlation effects in topological phases and their transitions is a cuttingedge area of research in recent condensed matter physics. We study topological quantum phase transitions (TQPTs) between doubleWeyl semimetals (DWSMs) and insulators, and argue that a novel class of quantum criticality appears at the TQPT characterized by emergent anisotropic nonFermi liquid behaviors, in which the interplay between the Coulomb interaction and electronic critical modes induces not only anisotropic renormalization of the Coulomb interaction but also strongly correlated electronic excitation. Using the standard renormalization group methods, large N_{f} theory and the ε=4−d method with fermion flavor number N_{f} and spatial dimension d, we obtain the anomalous dimensions of electrons (η_{f}=0.366/N_{f}) in large N_{f} theory and the associated anisotropic scaling relations of various physical observables. Our results may be observed in candidate materials for DWSMs such as HgCr_{2}Se4 or SrSi_{2} when the system undergoes a TQPT. 
Monday, March 4, 2019 9:36AM  9:48AM 
A06.00009: Fermi liquid corrections for nonequilibrium transport through an SU(N) Anderson impurity with arbitrary electron fillings Yoshimichi Teratani, Akira Oguri We extend a Fermiliquid description, which has recently been revisited to derive exact nonequilibrium transport formulas applicable to the particlehole asymmetric case [1,2], for studying the Anderson impurity model with N orbitals at low temperatures T and at low bias voltages eV. We also apply the formulas to the SU(N) symmetric case and calculate order T^{2} and (eV)^{2} contributions of the differential conductance dI/dV, by using the numerical renormalization group (NRG) approach and also the 1/(N1) expansion [3]. Our results, obtained in a wide range of electron fillings, show that contributions of threebody fluctuations that enter through nonlinear susceptibilities play an important role as a gate voltage varies away from the particlehole symmetric point where the impurity levels are halffilled. Furthermore, the contributions of three body fluctuations show an oscillatory behavior as gate voltage ε_{d} varies and, the three body fluctuations decrease as the number of the orbital N increases. 
Monday, March 4, 2019 9:48AM  10:00AM 
A06.00010: Outofequilibrium dynamics and thermalization across a solvable nonFermi liquid to Fermi liquid transition Arijit Haldar, Prosenjit Haldar, Sumilan Banerjee We study the nonequilibrium dynamics of an interacting model [1] having a quantum phase transition from a SachdevYeKitaev (SYK) nonFermi liquid(NFL) to a Fermi liquid(FL). The model has SYK fermions on N sites quadratically coupled to noninteracting peripheral fermions on M sites. The transition from the NFL (p < 1) to FL (p > 1) is obtained at p=1 by tuning the ratio p=M/N. We study the dynamics as a function of p, (a) after a quench where the coupling between initially disconnected SYK and peripheral fermions is suddenly switched on, and (b) during a slow quench when the coupling is slowly ramped over a duration τ. In the sudden quench, we find that a thermal state is reached in the NFL (p < 1) through collapserevival oscillations of the quasiparticle residue of the peripheral fermions. In the FL phase, the system fails to thermalize within the accessible time and shows multiple prethermal regimes. In the slow quench, the excitation energy generated has a powerlaw dependence ∼τ ^{−η} for intermediate τ, with a strong pdependent η having a minimum at the transition. At larger τ the powerlaw breaks down, along with adiabaticity, due to the initial residual entropy of the SYK fermions. [1] S. Banerjee and E. Altman, PRB 95, 134302 (2017). 
Monday, March 4, 2019 10:00AM  10:12AM 
A06.00011: Solvable lattice models for intermediate scale nonFermi liquid metals Debanjan Chowdhury, Senthil Todadri A number of strongly correlated materials, such as the ruthenates and cobaltates, display metallic nonFermi liquid (NFL) properties over a broad range of temperatures down to a low coherence scale, T_{coh}. The intermediate NFL regime displays anomalous transport properties, broad electronic spectral functions indicating the absence of sharp quasiparticles and is often accompanied by a finite extrapolated zero temperature entropy. Theoretically, examples of similar NFL metals can be obtained using higher dimensional generalizations of the solvable SYK model and have also been shown to arise in dynamical meanfield theory solutions of more realistic microscopic models. Going beyond these approaches, I will propose other models and setups where a broad incoherent metallic regime arises in the presence of a finite configurational entropy. 
Monday, March 4, 2019 10:12AM  10:24AM 
A06.00012: Conductivity of a compensated metal near a Pomeranchuk quantum critical point: the absence of mass renormalization Dmitrii Maslov, Songci Li The role of mass renormalization, m^{*}/m_{b}, in electron transport near a quantum critical point (QCP) is a nontrivial issue. According to a naive interpretation of the Drude formula, as electrons get heavier near a QCP, their electrical and thermal conductivities decrease. However, this picture has never been supported by an actual calculation. In this work, we employ a model case of a compensated metal near a Pomeranchuktype criticality. The advantage of this model is that it allows one to treat electrical and thermal conductivities on the same footing, without invoking umklapp scattering or any other channels of momentum relaxation which are extraneous to the electron system. By solving exactly the kinetic equation, we obtain explicit results for the electrical and thermal conductivities, and also for the viscosity of a twoband compensated metal. We show that mass renormalization factors cancel out with the Z factors, which renormalize the scattering probability, such that all the transport quantities contain the bare rather than renormalized electron masses. We also demonstrate how the same cancelation happens diagrammatically, on an example of the optical conductivity of a compensated metal. 
Monday, March 4, 2019 10:24AM  10:36AM 
A06.00013: Entanglement signatures of quantumtoclassical crossover of a Fermi surface Hassan Shapourian, Shinsei Ryu The entanglement entropy of free fermions with a Fermi surface is known to obey a logarithmic scaling and violate the area law in all dimensions. Here, we would like to see how thermal fluctuations affect the logarithmic scaling behavior. To this end, we analytically compute the bipartite entanglement negativity of a finitetemperature state and show that the coherent Fermi surface is gradually destroyed as a function of temperature and eventually turns into an incoherent classical system, where the entanglement is completely lost. We check that our analytical results agree with the numerical simulation of free fermions on a lattice. 
Monday, March 4, 2019 10:36AM  10:48AM 
A06.00014: StrongCoupling Study of Interlayer Pairing in Bilayer Composite Fermion Metals Luis Mendoza, Nicholas Evans Bonesteel We study the T=0 Eliashberg equations for interlayer pairing in the composite fermion description of the ν=1/2+1/2 quantum Hall bilayer system. In this description, composite fermions are coupled to two bosonic gauge fields which, in addition to leading to a breakdown of Fermi liquid theory, mediate a singular attractive interaction and a less singular repulsive interaction in the interlayer Cooper channel. Our solution of the T=0 Eliashberg equations includes both these pairing and pairbreaking effects, along with selfenergy effects. We compare our results with previous Eliashberg results which do not take selfenergy effects into account [1], and results obtained using the RG [2,3]. The connection between the RG and Eliashberg frameworks is also studied through the local approximation introduced in [4]. In particular we carry out the local approximation explicitly and compare with our results obtained from the full Eliashberg equations. 
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