Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K19: Precision Many Body Physics VIIFocus

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Sponsoring Units: DAMOP DCMP Chair: Ehsan Khatami, San Jose State University Room: BCEC 156C 
Wednesday, March 6, 2019 8:00AM  8:36AM 
K19.00001: Monte Carlo Studies of Quantum Critical Metals Invited Speaker: Erez Berg Metallic quantum critical phenomena are believed to play a key role in many strongly correlated materials, including high temperature superconductors. Theoretically, the problem of quantum criticality in the presence of a Fermi surface has proven to be highly challenging. However, it has recently been realized that many models used to describe such systems are amenable to numerically exact solution by quantum Monte Carlo (QMC) techniques, without suffering from the fermion sign problem. I will review the status of the understanding of metallic quantum criticality, and the recent progress made by QMC simulations, focusing on the cases of spin density wave and Ising nematic criticality. The results obtained so far will be described, as well as their implications for superconductivity, nonFermi liquid behavior, and transport in the vicinity of metallic quantum critical points. Some of the outstanding puzzles and future directions are highlighted. 
Wednesday, March 6, 2019 8:36AM  8:48AM 
K19.00002: Real time Quantum Monte Carlo for out of equilibrium strongly correlated systems. Corentin Bertrand, Antoine Maillard, Serge Florens, Olivier Parcollet, Xavier Waintal

Wednesday, March 6, 2019 8:48AM  9:00AM 
K19.00003: Infinite boundary conditions as a current source for impurity conductance in a quantum wire Adam Iaizzi, ChungYu Lo, Pochung Chen, YingJer Kao Developing nanoelectronic devices requires a detailed understanding of conduction in quantum wires. Numerical methods based on the density matrix renormalization group (DRMG) are excellent tools for studying onedimensional quantum systems, but studying finite biases and currents requires timedependent simulations, which remain challenging. Here we consider the problem of conductance across an impurity (or quantum dot) connected to metallic leads. Previous studies^{1,2} have used a finite wire with open boundary conditions, which suffers from strong finitesize effects. We use a powerful numerical method incorporating infinite boundary conditions^{3} (obtained from infinite DMRG^{4}) to simulate semiinfinite leads. We extract linear conductance from static correlation functions within a finitesize window that contains the impurity. Building on that, we use a timedependent method to extract conductance in the presence of finite bias. 
Wednesday, March 6, 2019 9:00AM  9:12AM 
K19.00004: Resonant Tunneling with Dissipation in a Spinfull Quantum Dot. Trevyn Larson, Gu Zhang, ChungTing Ke, MingTso Wei, Harold U Baranger, Gleb Finkelstein We study resonant tunneling through a nanotube quantum dot subject to a dissipative environment. It has been previously shown that in the spinless case, a quantum critical point is realized when the system is tuned onresonance with symmetric coupling to the leads. At that point, conductance at low temperatures reaches e^{2}/h and several scaling laws are observed. Here, we demonstrate a qualitatively different behavior in the case of a spinfull resonance. In particular, the positions of resonant peaks change in a nontrivial fashion as a function of temperature, which is attributed to the lack of the particlehole symmetry; and the peak height is not quantized and varies with dissipation strength. We argue that these signatures indicate the presence of the intermediate fixed point. 
Wednesday, March 6, 2019 9:12AM  9:24AM 
K19.00005: Quench dynamics of superconducting fluctuations and optical conductivity in a disordered system Aditi Mitra, Yonah S Lemonik There has been significant interest in the generation of very shortlived superconducting 
Wednesday, March 6, 2019 9:24AM  9:36AM 
K19.00006: Manybody Dynamic Structure Factors with Phase Space methods Jonathan Wurtz, Anatoli S Polkovnikov Recently there has been much interest in describing the behavior of stronglyinteracting quantum systems, especially equilibrium relaxation and hydrodynamic response. Intuitively, such behavior is classical, and should have an effective description with polynomial complexity as opposed to the exponential complexity of full quantum dynamics. This talk will detail work on one such semiclassical description, the Cluster Truncated Wigner Approximation, which approximates dynamics in a highdimensional classical phase space. Via sampling in this phase space, the method precisely reproduces both shorttime farfromequilibrium quantum dynamics and longtime thermal dynamics. In particular, we will show how using this method one can accurately compute the spin diffusion constant with the dynamic structure factor. 
Wednesday, March 6, 2019 9:36AM  9:48AM 
K19.00007: Berry's ansatz in Fock space: beyond random matrix theory for manybody quantum chaos Remy Dubertrand, JuanDiego Urbina, Klaus Richter Berry's ansatz of random superposition of vector basis to mimic the statistical properties of quantum states in classically chaotic systems, has been highly successfull for onebody systems. It is at the heart of the original justification for the eigenstate thermalisation hypothesis (ETH) for manybody quantum systems. We detail its use in manybody Fock space using recent developments in manybody semiclassical techniques for Bose Hubbard models. Quantitative predicitions for 2point correlations in Fock space are given, which agree very well with numerics. This study highlights how semiclassical techniques can be efficient for manybody chaos beyond the universal regime of random matrix theory. 
Wednesday, March 6, 2019 9:48AM  10:00AM 
K19.00008: Floquet behavior of correlated systems with lightmatter coupling Mona Kalthoff, James Freericks, Goetz S Uhrig, Dante Kennes, Angel Rubio, Michael Sentef Periodically driven nonequilibrium manybody systems have a quasienergy spectrum which can be tailored by external driving fields, known as Floquet engineering of desired system properties [Sentef et al., Nat. Comm. 6, 7047 (2015); Uhrig et al, arXiv:1808.10199 (2018)]. However, continuous periodic driving is not realizable in pumpprobe experiments in solids. For instance it is not clear which criteria a pulse has to meet for a system exposed to a pulsed drive to approach the Floquet limit of a periodically driven system. However, there are analytical results for noninteracting band electrons in infinite dimensions [Kalthoff et al., Phys. Rev. B 98, 035138 (2018)]. Moreover we discuss tDMRG results for interacting 1D chains in the charge density wave phase to study the emergence of Floquet behavior for realistic pulse shapes. This builds on the recently proposed Floquet engineering in quantum chains [Kennes et al., Phys. Rev. Lett. 120, 127601(2018)]. 
Wednesday, March 6, 2019 10:00AM  10:12AM 
K19.00009: Ultrafast manybody correlations in an excitonic insulator out of equilibrium Riku Tuovinen, Denis Golez, Michael Schüler, Philipp Werner, Martin Eckstein, Michael Sentef A fast time propagation method for nonequilibrium Green's functions [1] based on the generalized KadanoffBaym Ansatz (GKBA) [2] is applied to a lattice system with a symmetrybroken equilibrium phase, namely an excitonic insulator [3]. The adiabatic preparation of a correlated symmetrybroken initial state from a HartreeFock wave function within GKBA is assessed by comparing with a solution of the imaginarytime Dyson equation [4]. We find that it is possible to reach a symmetrybroken correlated initial state with nonzero excitonic order parameter by the adiabatic switching procedure. We discuss under which circumstances this is possible in practice within reasonably short switching times. We further investigate the outofequilibrium dynamics of competing orders and how the balance between them could be controlled by laser driving [5]. 
Wednesday, March 6, 2019 10:12AM  10:24AM 
K19.00010: Realtime quantum Monte Carlo for the spinboson model Olga Goulko, Guy Cohen, Moshe Goldstein The spin–boson model consists of a twostate system coupled to a bath of noninteracting harmonic modes. This fundamental, yet nontrivial model describes dissipation in a quantum system and can be mapped to an impurity coupled to interacting electron leads. Using the inchworm Monte Carlo algorithm we are able to precisely compute various nonequilibrium properties of the spinboson model, such as the realtime evolution of the population difference between the two states at different temperatures, different forms of the bosonic bath spectrum, and different values of the spinbath coupling, including the strong coupling regime. We also discuss how to calculate the heat current through the system coupled to two baths at different temperatures using full counting statistics. 
Wednesday, March 6, 2019 10:24AM  10:36AM 
K19.00011: Heating Dynamics in a Periodically Driven SYKModel Clemens Kuhlenkamp, Simon Weidinger, Michael Knap Periodically driven quantum matter can realize exotic dynamical phases that do not even exist in equilibrium. In order to understand how ubiquitous and robust these phases are, it is important to understand the heating dynamics of generic interacting quantum systems. We study the thermalization and heating dynamics in a generalized SYKmodel subjected to a periodic drive, which realize a FermiLiquid (FL) to NonFL crossover at a certain energy scale. Using an exact field theoretic approach we determine two regimes in the heating dynamics. At energies above the crossover scale the system is efficiently thermalizing and heats up exponentially. This crossover in the heating dynamics may be experimentally studied by measuring the absorption of THz laser light that impinges an irregularly shaped graphene flake in a strong magnetic field, which has been proposed to realize exotic SYK physics. 
Wednesday, March 6, 2019 10:36AM  10:48AM 
K19.00012: Entropy of the (1+1)dimensional directed percolation Kenji Harada We investigate the informational aspect of a (1+1)dimensional directed percolation which can be regarded as a reactiondiffusion process in a onedimensional system and is a canonical model of a nonequilibrium continuous phase transition into an absorbing state. Using a tensor network scheme based on a mapping between a state probability distribution and a wave function, we can numerically calculate a time evolution of a state probability distribution. Although the density of active sites has no singular behavior, there is a new singular point in the conventional active phase at which the dynamical behavior of the entanglement entropy changes. The Rényi entropy has a cusp at the same point. The Rényi entropy also shows a universal relaxation at the critical point of the conventional absorbing phase transition. 
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