Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A44: Correlated Chains and 1D SystemsLive

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Sponsoring Units: DCMP Chair: Yonko Millev, American Physical Society 
Monday, March 15, 2021 8:00AM  8:12AM Live 
A44.00001: Dynamics, Entanglement, and the Classical Point in the TransverseField XXZ Chain Cs_{2}CoCl_{4} Pontus Laurell, Allen Scheie, Chiron J. Mukherjee, Michael M. Koza, Mechthild Enderle, Zbigniew Tylczynski, Satoshi Okamoto, Radu Coldea, David A Tennant, Gonzalo Alvarez We investigate the quantum phase transition in the S=1/2 transversefield XXZ spin chain using multiple entanglement measures and witnesses. As the field strength increases, this system passes through two quantum critical points of different universality classes, as well as a classical point. Consequently, the entanglement can be tuned by simply changing the magnetic field. Using DMRG calculations we study the entanglement entropy, onetangle, twotangle, and quantum Fisher information. We also report highresolution inelastic neutron scattering data on Cs_{2}CoCl_{4}, and the experimental extraction of entanglement witnesses from the neutron data. We find that quantum Fisher information values extracted from experiment and simulation show good agreement, demonstrating it is an experimentally viable probe of entanglement. 
Monday, March 15, 2021 8:12AM  8:24AM Live 
A44.00002: Spin dynamics in the transversefield Ising chain at nonzero temperature Jiahao Yang, Marton Kormos, Jianda Wu, Qimiao Si There has been considerable recent progress in elucidating the dynamics of the transversefield Ising chain (TFIC) and in the search for candidate materials. Here, we study the spin dynamical structure factor in the quantum disordered region of TFIC. The study is carried out both in the continuum limit via a fieldtheory method and in the lattice model. We determine the local spin dynamics as a function of both frequency and temperature, and identify an unusual logarithmic correction factor. We discuss how our results can evince material realization of the TFIC universality. 
Monday, March 15, 2021 8:24AM  8:36AM Live 
A44.00003: Spin dynamics of a perturbed quantum critical Ising chain Xiao Wang, Haiyuan Zou, Kristóf Hódsági, Marton Kormos, Jianda Wu Nearcritical system can exhibit exotic excitations. When the quantum critical transversefield Ising chain is perturbed by a longitudinal field, a quantum integrable model emerges with massive excitations described by the exceptional E_{8 }Lie algebra. Using analytical form factors of the quantum E_{8} integrable model, we systematically study the spin dynamic structure factor of the perturbed quantum critical Ising chain, where particle channels with total energy up to 5m_{1} (m_{1} being the mass of the lightest E_{8} particle) are exhausted. Besides significant single particle channels’ contribution to the dynamic spectrum, different multiparticle channels also exhibit rich features in the continuum region with a cascade of bumping peaks, which can serve as a solid base for guiding the material realization of the E_{8} model. Our results support the recent series of experimental realizations of the quantum E_{8} model in the material BaCo_{2}V_{2}O_{8}, laying down a concrete material ground to study physics beyond integrability. 
Monday, March 15, 2021 8:36AM  8:48AM Live 
A44.00004: Onsager's scars in disordered spin chains Naoyuki Shibata, Nobuyuki Yoshioka, Hosho Katsura The Eigenstate Thermalization Hypothesis (ETH) is a plausible scenario of the thermalization of isolated quantum systems. Although there is no rigorous proof, it is widely believed to hold for a large class of nonintegrable systems. However, recent experiments with Rydberg atoms [1] observed robust periodic revivals from certain initial states, implying anomalously slow thermalization, even though the system is nonintegrable. This athermal phenomenon called quantum manybody scars (QMBS) results from the existence of ETHviolating eigenstates [2]. 
Monday, March 15, 2021 8:48AM  9:00AM Live 
A44.00005: Emptiness Formation Probability in 1D Quantum Liquids. HsiuChung Yeh, Alex Kamenev We study emptiness formation probability (EFP) in interacting 1D Bose liquids. That is the probability that a snapshot of its ground state reveals exactly zero number of particles within the interval x < R. For a weakly interacting liquid there is parametrically wide regime 1/n < R < ξ (here n is the average density and ξ is the healing length), where EFP exhibits a nontrivial crossover from the Poisson to the Gaussian behavior. We employ the instanton technique [A. Abanov, 2004] to study quantitative details of these regime and compare it with previously reported limited cases. 
Monday, March 15, 2021 9:00AM  9:12AM Live 
A44.00006: Adiabatic formation of bound states in the 1d Bose gas Alvise Bastianello, Rebekka Koch, JeanSebastian Caux In this talk, I discuss the bound state formation in the 1d Bose gas out of equilibrium due to interaction changes from the repulsive to the attractive regime. In the case of adiabatic protocols, the populations of the bound states can be exactly determined thanks to a recently devised hydrodynamic approach to integrable models, known as Generalized Hydrodynamics. Applications to the stateofthearts cold atoms experiments are shortly discussed. 
Monday, March 15, 2021 9:12AM  9:24AM Live 
A44.00007: Violation of WiedemannFranz law in strongly interacting onedimensional electrons Kamal Sharma We present our study on the violation of WiedemannFranz law in onedimensional strongly interacting spinless electron systems. The Luttinger liquid theory describes the lowenergy excitations of a gapless onedimensional quantum manybody systems. The defining feature of a Luttinger liquid is its wellbehaved collective excitations, analogous to sound waves, with linear bosonic dispersion. However, real onedimensional quantum systems demonstrate a nonlinear interacting quantum liquid behavior that is different from either Luttinger liquids (1D) or Fermi liquids (2D). Further, such a system violates the Wiedemann Franz law (κ ∝ σΤ, where κ is the thermal conductance and σ is the electrical conductance). This is because any arbitrarily weak interaction potential between Luttinger liquid excitations leads to divergences in the scattering amplitude between Luttinger liquid excitatations. We adopt the onedimensional Wigner crystal as the strongly interacting regime of Luttinger liquid and show that the violation of the WiedemannFranz law can be demonstrated by calculating the correction to thermal conductance due to scattering between bosonic excitations in the presence of a weak nonlinearity in dispersion. 
Monday, March 15, 2021 9:24AM  9:36AM Live 
A44.00008: Hydrodynamic descriptions of multicomponent quantum fluids in onedimensional systems Yanqi Wang, Joel Ellis Moore Hydrodynamic theories have been widely used in studying the transport problem of interacting electronic systems with minimal momentum relaxation. A strongly interacting plasma of linearly dispersing electron and hole excitations, also known as a Dirac fluid, can be captured by relativistic hydrodynamics. The most studied example of a Dirac fluid is twodimensional graphene at charge neutrality, which in the absence of impurities has diverging thermal conductivity but finite electric conductivity, leading to violations of the WiedemannFranz law. It is natural to ask which quantum liquids in one dimension, where additional nonpertubative methods are available, can possess similar transport properties to chargeneutral graphene, and what the leading corrections to this behavior are in realistic systems. In this work, within the frame of hydrodynamics, we investigate a generic Luttinger liquid theory (i.e., incorporating integrabilitybreaking perturbations) which is closely related to the twodimensional Dirac fluid in graphene, with various transport properties calculated. 
Monday, March 15, 2021 9:36AM  9:48AM Live 
A44.00009: Viscous Properties of OneDimensional Fermi Gases Wade DeGottardi, K. A. Matveev We present recent work on the hydrodynamics of onedimensional and quasionedimensional Fermi gases. A particular focus is on the bulk viscosity, a transport coefficient which is essential to the application of hydrodynamics. This classical description breaks down at frequencies large compared with the rate of fermion backscattering. This regime, which has been the subject of recent theoretical interest, is described by twofluid behavior. As in the case of superfluid helium4, the twofluid regime requires not one but three bulk viscosities, which we calculate in the limit of weak interactions. 
Monday, March 15, 2021 9:48AM  10:00AM Live 
A44.00010: LongRange Falikov Kimball Model in One Dimension: Phase Transition, DisorderFree Localisation and Delocalisation Thomas Hodson, Josef Wilsher, Johannes Knolle Both disorder or interactions may turn metals into insulators. One of the simplest settings to study this physics is given by the FalikovKimball model describing itinerant fermions interacting with a classical background field. Despite the translational invariance of the model, inhomogenous configurations of the background field give rise to effective disorder physics leading to a rich phase diagram in two (or higher dimensions) with finite temperature charge density wave (CDW) transitions and interactiontuned Anderson versus Mott localized phases. Here, we propose a generalised \ac{FK} model in one dimension with longrange interactions which shows a similarly rich phenomenology. In the high temperature phase, the fermions propagate against a disordered background field which leads to exponential localisation of all eigenstates. Below the CDW transition enabled by the powerlaw interactions, the thermal fluctuations of the order parameter induce correlated disorder which leads to the coexistence of localised and delocalised states at separate energies. Using a combination of exact diagonalisation and \acl{MCMC} we map out the phase diagram and compute the energy resolved localisation properties of the fermions. 
Monday, March 15, 2021 10:00AM  10:12AM Live 
A44.00011: True Bilayer Exciton Condensate of OneDimensional Electrons Adrian Kantian We theoretically predict that a true bilayer exciton condensate, characterized by offdiagonal longrange order and global phase coherence, can be created in onedimensional solid state electron systems. The mechanism by which this happens is to introduce a single particle hybridization of electron and hole populations, which locks the phase of the relevant mode and hence invalidates the MerminWagner theorem. Electronhole interactions then amplify this tendency towards offdiagonal longrange order, enhancing the condensate properties by more than an order of magnitude over the noninteracting limit. We show that the temperatures below which a substantial condensate fraction would form could reach hundreds of Kelvin, a benefit of the weak screening in onedimensional systems. 
Monday, March 15, 2021 10:12AM  10:24AM Live 
A44.00012: Farfromequilibrium dynamics in open fermion chains Miguel Moreira de Oliveira, Pedro Ribeiro, Stefan Kirchner Recent attention has been paid to the study of open systems coupled to Markovian reservoirs using MPS techniques. 
Monday, March 15, 2021 10:24AM  10:36AM 
A44.00013: Continuous NéelVBS Quantum Phase Transition in NonLocal onedimensional systems with SO(3) Symmetry ChaoMing Jian, Yichen Xu, Xiaochuan Wu, Cenke Xu One dimensional (1d) interacting systems with local Hamiltonians can be studied with various welldeveloped analytical methods. Recently novel 1d physics was found numerically in systems with either spatially nonlocal interactions, or at the 1d boundary of 2d quantum critical points, and the critical fluctuation in the bulk also yields effective nonlocal interactions at the boundary. This work found that the original (1+1)d boundary conformal field theory of a 2d SPT state is unstable due to coupling to the boundary avatar of the bulk quantum critical fluctuations. When the bulk is fixed at the orderdisorder quantum critical point, we find that by tuning one parameter at the boundary, there is a generic direct transition between the valence bond solid (VBS) order and another phase with potentially a long range Néel order. This transition is very similar to the NéelVBS transition recently found in numerical simulation of a spin1/2 chain with nonlocal spatial interactions. 
Monday, March 15, 2021 10:36AM  10:48AM Live 
A44.00014: Attenuation of energy relaxation in chiral onedimensional quantum channels Stefan Fischer, Bernd Rosenow, Yuval Gefen, Yigal Meir In order to probe energy relaxation in a onedimensional chiral channel, we consider the injection of a dilute beam of electrons at a sharplydefined energy above the channel's Fermi sea. The injected electrons undergo finiterange interactions with channel electrons. In order to obtain the energy distribution in the channel as a function of the injected electrons' propagation time, we perform a nonperturbative calculation using bosonization. In this approach, low energy excitations in the channel (plasmons) propagate at a constant velocity that is higher than the injected electrons' velocity. We find that injected electrons lose only about one quantum of energy, measured in units of the ratio of plasmon velocity and interaction range. To investigate the resulting energy distribution also in the presence of a nonlinear plasmon dispersion relation, we present a solution of the problem that is exact in the semiclassical limit, applicable when the injection energy is much higher than the typical plasmon energy, and when the energy loss is not too large. 
Monday, March 15, 2021 10:48AM  11:00AM Not Participating 
A44.00015: Disorderinduced Enhancement of Entanglement Growth in One Dimension: Information Leakage at the scale of localization length ROOPAYAN GHOSH, Arnab Das When a group of compactly packed free fermions is allowed to spread over an empty one dimensional lattice, the spreading particles can create entanglement between different parts of the lattice. We show, though breaking of translational invariance (TI) of the lattice by disorder slows down the spreading of local observables, the entanglement entropy of a subsystem can nonetheless receive a remarkable enhancement as long as the subsystem lies within the singleparticle localization length. We show, the main mechanism behind this enhancement is the reentrant exchange of particles between the subparts due to transport of mutual information due to back scattering. We discuss the length and time scales relevant to the phenomenon. We study the phenomenon for breaking of TI by both quasiperiodic and random potentials. We further explore the effect of randomness only in the initial state. This also exhibits a similar enhancement effect even in a TI lattice. We also touch upon the special case of periodic potential, where qualitatively similar phenomenology emerges, though the coherence in the back scattering in this case leads to effects not captured by our simple yet generic picture. 
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