Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y48: Statistical and Nonlinear Physics II |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Daniel Lathrop, University of Maryland, College Park Room: BCEC 251 |
Friday, March 8, 2019 11:15AM - 11:27AM |
Y48.00001: The Ising Model in Curved Geometries Nikolas Breuckmann, Ananda Roy, Benedikt Andreas Placke The study of statistical mechanics in curved geometries has recently gained an increasing amount of attention. Particularly the Ising model in negatively curved spaces has been studied as a mean to understand exotic crystals, soft-matter and field theories in Anti-de Sitter spaces. |
Friday, March 8, 2019 11:27AM - 11:39AM |
Y48.00002: Strong randomness criticality in the scratched-XY model Zhiyuan Yao, Tobias Pfeffer, Lode Pollet We study the finite-temperature superfluid--normal-liquid classical phase transitions in a disordered two-dimensional XY model with power law distributed "scratch"-like bond disorder. While for weak disorder the transition is of Berezinskii-Kosterlitz-Thouless type, the transition in the strong disorder regime is in a different universality class with a non-universal jump of the superfluid stiffness. We show this new criticality can be described by the asymptotically exact theory of superfluid-insulator quantum phase transition in one-dimensional disordered boson systems and discuss possible experimental realizations. |
Friday, March 8, 2019 11:39AM - 11:51AM |
Y48.00003: Violation of a universal changeover in two-dimensional Potts models Nir Schreiber, Reuven Cohen, Simi Haber, Gideon Amir We present a novel combinatorial approach which allows the determination of the critical temperature and the phase transition order of Potts models with multi-site interaction. Applying this approach to the hexagonal lattice, it is demonstrated that Potts models with local, range independent interaction may changeover from a continuous to a discontinuous phase transition, at a marginal value q_{c}≤3. Our theory is substantiated by Monte-Carlo simulations. In particular, it is numerically indicated that the system undergoes a first order transition for q=3. The latter is in agreement with a further prediction of q_{c}≤2, established under a mild assumption related to the asymptotic growth of hexagonal lattice animals. Our findings are in contrast to known cases where q_{c}=4 which were believed to represent a universal |
Friday, March 8, 2019 11:51AM - 12:03PM |
Y48.00004: Non-universal Dynamics of Three-Dimensional Magnetic Systems With Heisenberg Interaction Riya Nandi, Uwe Claus Tauber We numerically investigate the non-equilibrium critical dynamics in three-dimensional isotropic Heisenberg antiferromagnets. To account for the reversible terms arising from the microscopic dynamics of the system, we employ a hybrid simulation algorithm that combines reversible spin precession with relaxational Kawasaki spin exchange processes. We verify the dynamic exponent, and obtain a suitable aging scaling window. We observe and thus validate an older renormalization group prediction that, while the critical aging collapse exponent assumes universal value, the temporal decay exponent is found to be non-universal and dependent on the initial distribution of the spins. |
Friday, March 8, 2019 12:03PM - 12:15PM |
Y48.00005: Exact many-body quantum scar states with topological properties in dimensions 1, 2, and 3 Seulgi Ok, Kenny Choo, Christopher M Mudry, Claudio Castelnovo, Claudio Chamon, Titus Neupert We provide a general construction of exact excited states in a class of certain non-integrable conserved quantum many-body Hamiltonians. These states have area law entanglement entropy, while they are spectrally embedded in states with volume law scaling. Our construction applies to models in arbitrary dimensions, and we exemplify it for scar states with properties usually associated to gapped ground states of symmetry protected topological phases or topologically ordered phases of matter, including the respective degeneracies. |
Friday, March 8, 2019 12:15PM - 12:27PM |
Y48.00006: Stability of quantum statistical ensembles with respect to random local measurements Boris Fine, Walter Hahn We define a quantum statistical ensemble as 'stable', if a small number of local measurements cannot significantly modify the total-energy distribution representing the ensemble. This stability criterion is applied to lattices of spins-1/2, for which different measures of the quantum ensemble stability are investigated. In the context of the foundations of quantum statistical physics, our results justify the use of statistical ensembles with narrow energy distributions such as canonical or microcanonical ensembles. |
Friday, March 8, 2019 12:27PM - 12:39PM |
Y48.00007: Quantum Heat Machines with Trapped Ions Suman Chand, Asoka Biswas Quantum heat machines (QHM) are those quantum systems that convert heat into the useful form of work. Specific kinds of QHMs, namely the heat engines and the refrigerators, among others have been studied in quantum regimes, using discrete strokes or continuous strokes. Heat engines take the heat from a hot bath, deliver a certain amount of work, and release heat to the cold bath. In most of the proposals of QHMs it is assumed that the hot bath and the cold bath are physically separated and can be switched on or off in a controlled way, just as in the case of their classical counterpart. In quantum regime, however, the interaction between the system and the bath is never switched off. Therefore, newer strategies are required for a QHM that can be implemented in a realistic scenario, and also within the quantum framework. Here, we show how one can implement different strokes of an Otto engine, using a single trapped ion. Using two ions, one can even build a refrigerator. Further, we study how a QHM performs across the critical value of an external parameter, pertaining to the quantum phase transition |
Friday, March 8, 2019 12:39PM - 12:51PM |
Y48.00008: Generalized Bogoliubov-Hartree-Fock Theory - Magnetic order and superconductivity in extended Hubbard models Chris Koschenz, Carsten Timm We present a generalized Bogoliubov-Hartree-Fock theory, which allows to study magnetic ordering, charge ordering, and superconductivity on the same footing and gives additional information about the so-called mixed phases [1]. These phases emerge in parameter ranges where the system is potentially strongly affected by fluctuations and cannot be described by any set of usual Hartree-Fock states (Slater determinants) [1,2]. Furthermore, we show how to obtain the self-consistent set of order parameters in the normal and BCS states by straightforward unrestricted global minimization of the appropriate Landau functional [3]. This method allows us to study the coexistence and competition of various magnetic and superconducting order and can be used to study the possibility of additional phase transitions in the coexistence regime. |
Friday, March 8, 2019 12:51PM - 1:03PM |
Y48.00009: Enhancing the predictability and retrodictability of stochastic processes Nathaniel Rupprecht, Dervis Can Vural Scientific inference involves obtaining the unknown properties or behavior of a system in the light of what is known, typically, without changing the system. Here we propose an alternative to this approach: a system can be modified in a targeted way, preferably by a small amount, so that its properties and behavior can be inferred more successfully. For the sake of concreteness we focus on inferring the future and past of Markov processes and illustrate our method on two classes of processes: diffusion on random spatial networks, and thermalizing quantum systems. |
Friday, March 8, 2019 1:03PM - 1:15PM |
Y48.00010: Anomalous thermal relaxation and the Mpemba effect of Langevin particles Matt Walker, Marija Vucelja The Mpemba effect is an anomalous relaxation process in which a system starting at a hot temperature cools down faster than an identical system starting at an initially lower temperature when both are coupled to an even colder bath. The effect has been observed in water, clathrate hydrates, magnetic alloys, and driven granular gases. We search for an analogous to Mpemba phenomenon for the case of a Langevin particle diffusing and advecting on a potential energy landscape. The particle is diffusing with a diffusion constant, that corresponds to a temperature that is lower than specified by the initial condition. We study the Mpemba effect, or non-monotonic thermal relaxation, as a function of parameters specifying the potential landscape. |
Friday, March 8, 2019 1:15PM - 1:27PM |
Y48.00011: Anomalous diffusion and the Moses effect in an aging deterministic model Vidushi Adlakha, Philipp G. Meyer, Holger Kantz, Kevin E Bassler We show that the anomalous diffusive behavior found in an aging system can be decomposed into three fundamental constitutive causes. A model process that is a sum of increments that are iterates of a chaotic dynamical system, the Pomeau-Manneville map, is examined. The increments can have long-time correlations, fat-tailed distributions and be non-stationary. Each of these properties can cause anomalous diffusion through what is known as the Joseph, Noah and Moses effects, respectively. The model can have either sub- or super-diffusive behavior, which we find is generally due to the combination of the three effects. Scaling exponents quantifying each of the three constitutive effects are calculated using analytic methods and confirmed with numerical simulations. They are then related to the scaling of the distribution of the process through a scaling relation. The work also discusses the importance of Moses effect in the anomalous diffusion of experimental systems. |
Friday, March 8, 2019 1:27PM - 1:39PM |
Y48.00012: Universal First-Passage-Time Distribution of Non-Gaussian Currents Shilpi Singh, Paul Menczel, Dmitry S Golubev, Ivan Khaymovich, Joonas T Peltonen, Christian Flindt, Keiji Saito, Édgar Roldán, Jukka P Pekola I present our recent work on the fluctuations of the time elapsed until the electric charge transferred through |
Friday, March 8, 2019 1:39PM - 1:51PM |
Y48.00013: Electromagnetic properties of random materials Pouyan Karimi, Martin Ostoja-Starzewski Scale dependence bounds on the electromagnetic properties are studied in the setting of spatially random linear materials with statistically homogeneous and spatially ergodic random microstructures. First, from the Hill-Mandel homogenization conditions adapted to electric and magnetic fields, uniform boundary conditions are formulated for a statistical volume element (SVE). From these conditions, rigorous bounds are obtained on the macroscale (effective) electrical permittivity and magnetic permeability. Using computational electromagnetism methods, these bounds are obtained through numerical simulations for composites of two types: (i) 2D random checkerboard (two-phase) microstructures and (ii) 2D Gaussian correlated microstructure. The simulation results demonstrate a convergence of these bounds to the effective properties with increasing length scales. |
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