Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D14: Systems Far From Equilibrium |
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Sponsoring Units: GSNP Chair: H. George E. Hentschel, Emory University Room: D227 |
Monday, March 21, 2011 2:30PM - 2:42PM |
D14.00001: Fluctuation Relations for Currents Nikolai Sinitsyn, Alexei Akimov, Vladimir Chernyak, Michael Chertkov We consider a non-equilibrium statistical system on a graph or a network. Identical particles are injected, interact with each other, traverse, and leave the graph in a stochastic manner described in terms of Poisson rates, possibly strongly dependent on time and instantaneous occupation numbers at the nodes of the graph. We show that the system demonstrates a profound statistical symmetry, leading to new Fluctuation Relations that originate from the supersymmetry and the principle of the geometric universality of currents rather than from the relations between probabilities of forward and reverse trajectories. [Preview Abstract] |
Monday, March 21, 2011 2:42PM - 2:54PM |
D14.00002: Aging in coarsening ferromagnets with site and bond disorder Hyunhang Park, Michel Pleimling Aging processes during phase ordering are studied in the random-site and random-bond Ising models in two dimensions through Monte-Carlo simulations. The dynamical correlation length $L(t)$ is numerically determined and the behavior of various two-time quantities is investigated. For both models deviations of $L(t)$ from an algebraic growth law $L(t) \sim t^{1/z}$ are observed. Using the correct form of $L(t)$ a simple scaling picture is recovered for the studied disordered ferromagnets in the coarsening regime. Thus various two-time quantities, as for example the autocorrelation function, the space-time correlation function and the time integrated linear response, show a scaling behavior that is fully consistent with simple aging [1]. The similarities and differences between the site-disordered and the bond-disordered models are discussed.\\[4pt] [1] H. Park and M. Pleimling, Phys. Rev. B {\bf 82}, 144406 (2010). [Preview Abstract] |
Monday, March 21, 2011 2:54PM - 3:06PM |
D14.00003: Nonequilibrium phase transition in a driven Potts model with friction Michel Pleimling, Ferenc Igl\'{o}i, Lo\"Ic Turban We consider magnetic friction between two systems of $q$-state Potts spins which are moving along their boundaries with a relative constant velocity $v$. Due to interaction between the surface spins there is a permanent energy flow and the system is in a steady state which is far from equilibrium. The problem is treated analytically in the limit $v=\infty$ (in one dimension, as well as in two dimensions for large-$q$ values) and for $v$ and $q$ finite by Monte Carlo simulations in two dimensions. Exotic nonequilibrium phase transitions take place, the properties of which depend on the type of phase transition in equilibrium. When this latter transition is of first order, a sequence of second- and first-order nonequilibrium transitions can be observed when the interaction is varied [1].\\[4pt] [1] F. Igl\'{o}i, M. Pleimling, and L. Turban, arXiv:1010.0738. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D14.00004: Aging dynamics for the driven lattice gas George L. Daquila, Uwe C. T\"auber We numerically investigate the two-time behavior of the density-density auto-correlation function in driven lattice gases with particle exclusion and periodic boundary conditions in one, two, and three dimensions using precise Monte Carlo simulations. Starting from strongly correlated initial conditions we investigate the relaxation towards the nonequilibrium steady state. We obtain simple aging scaling behavior in one, two, and three dimensions. The simulation data confirm the density auto-correlation aging exponents determined from simple scaling arguments. For the one-dimensional case we connect with the KPZ surface growth model and establish a relation between the density-density and known height-height auto-correlation aging exponents. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D14.00005: Effect of size distribution on metastability in magnetic nanoparticles Yoh Yamamoto, Kyungwha Park Magnetic nanoparticles that have been synthesized using various methods have size distributions. This results in distributions in the magnetic anisotropy of magnetic nanoparticles. Considering the particle size distributions, we investigate metastability in magnetic nanoparticles at low temperatures. To model this system, we use a spin $S=1$ ferromagnetic Blume-Capel model on a square lattice with periodic boundary conditions. The particle size distribution is incorporated in the model such that the uniaxial magnetic anisotropy parameter has a Gaussian distribution. We perform kinetic Monte Carlo simulations of the Blume-Capel model with the Glauber dynamic to explore magnetization relaxation in the regime where a single droplet of flipped spins forms a critical droplet. We present the lifetime of the metastable state as a function of temperature and standard deviation of the magnetic anisotropy distribution as well as a finite-size effect on the lifetime. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D14.00006: Phase Diagram for a 2-D Two-Temperature Diffusive XY Model Matthew Reichl, Charo Del Genio, Kevin E. Bassler Using Monte Carlo simulations, we determine the phase diagram of a diffusive two-temperature conserved order parameter XY model. When the two temperatures are equal the system becomes the equilibrium XY model with the continuous Kosterlitz-Thouless (KT) vortex-antivortex unbinding phase transition. When the two temperatures are unequal the system is driven by an energy flow from the higher temperature heat-bath to the lower temperature one and reaches a far-from-equilibrium steady state. We show that the nonequilibrium phase diagram contains three phases: A homogenous disordered phase and two phases with long range, spin texture order. Two critical lines, representing continuous phase transitions from a homogenous disordered phase to two phases of long range order, meet at the equilibrium KT point. The shape of the nonequilibrium critical lines as they approach the KT point is described by a crossover exponent $\varphi = 2.52 \pm 0.05$. Finally, we suggest that the transition between the two phases with long-range order is first-order, making the KT-point where all three phases meet a bicritical point. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D14.00007: Avalanches in gauge theories Stefanos Papanikolaou I consider the non-equilibrium behavior of disordered systems which contain a residual gauge symmetry. Remarkably, in this limit each avalanche is a Wilson loop of the associated gauge theory. Such gauge invariant avalanches present interesting critical behavior that we characterize. Also, I show that, when the gauge symmetry is violated, the behavior drastically changes. Finally, the relation of these results to current experimental efforts on spin ice compounds is discussed. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D14.00008: A framework for studying biased stochastic dynamics in continuous space S.M. Ali Tabei, Ye Tian, Martin Tchernookov, Aaron Dinner Typically in the formalism of large deviation functions the biased dynamics are studied in a discrete space. However, in many realistic stochastic systems dynamics take form in a continuous rather than a discrete space. In recent work it was shown that the biased dynamics for continuous-space models can be calculated using transition path sampling: unbiased trajectories were generated by shooting with the original dynamics from an existing path and then accepted or rejected to obtain the biased path ensemble. Here, we instead develop a way to bias continuous-space dynamics directly in the form of a biased Langevin equation. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D14.00009: Measured first-passage-time distributions for a high-dimensional system: noise-induced current switching in semiconductor superlattices Yuriy Bomze, Holger T. Grahn, Rudolf Hey, Stephen W. Teitsworth We report the experimental measurement of first-passage-time distributions associated with current switching in weakly-coupled GaAs/AlAs superlattices, in a regime of nonlinear electronic transport where the static current-voltage ($I - V$) curves exhibit multiple branches and bistability. Precision, high bandwidth current switching data are collected in response to sequential steps in applied voltage to a final voltage $V_f$ near to the voltage $V_{th}$ corresponding to the end of a particular branch. For initial state preparation, a double step procedure is used to insure that the system is close to the true metastable state. For a range of $V_f$ values, switching times reveal large stochastic fluctuations driven by internal shot noise. For smaller times ($<$ 3$\mu$s), the switching time distributions show exponential tails, as expected for activated escape from an initial metastable state. However, at larger times ($>$ 10 $\mu$s), the distributions exhibit power law tails (with exponent ranging from -2 to -1, and dependent on $|V_f -V_{th}|$). Possible sources for the power law decay include collective effects and the presence of multiple escape trajectories. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D14.00010: Non-equilibrium Thermodynamics: Residual Entropy, Internal Variables, Maxwell Relations, and the Prigogine-Defay Ratio Puru Gujrati We extend a recently formulated [Phys. Rev. E 81, 051130 (2010)] non-equilibrium thermodynamic approach to an inhomogeneous system consisting of many smaller subsystems, each in internal equilibrium; their relative motions result in viscous effects. The correct Gibbs free energy of a subsystem contains the temperature and pressure of the medium, making our approach an extension of the classical non-equilibrium thermodynamics due to de Donder. The additivity of entropy requires quasi-independence of subsystems, so that the energy also becomes additive. We use Gibbs' entropy of the isolated system to derive the entropy for the system even when the latter is out of equilibrium. We use this entropy to discuss the residual entropy when the system is confined to one of the components in the phase space. The approach is extended to include internal variables that cannot be controlled by the observer during non-equilibrium evolution. We then identify the form of non-equilibrium Maxwell relations. We apply our formalism to evaluate the Prigogine-Defay ratio in glasses, which is found to be, in general, different from 1 at the apparent glass transition, as is normally seen in experiments. [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D14.00011: Generalized Gibbs distribution and energy localization in the semiclassical FPU problem Rafael Hipolito, Ippei Danshita, Vadim Oganesyan, Anatoli Polkovnikov We investigate dynamics of the weakly interacting quantum mechanical Fermi-Pasta-Ulam (qFPU) model in the semiclassical limit below the stochasticity threshold. Within this limit we find that initial quantum fluctuations lead to the damping of FPU oscillations and relaxation of the system to a slowly evolving steady state with energy localized within few momentum modes. We find that in large systems this state can be described by the generalized Gibbs ensemble (GGE), with the Lagrange multipliers being very weak functions of time. This ensembles gives accurate description of the instantaneous correlation functions, both quadratic and quartic. Based on these results we conjecture that GGE generically appears as a prethermalized state in weakly non-integrable systems. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D14.00012: Zero Droplet Stiffness Exponent: Probing Short Range Spin Glasses with Avalanches Induced by Long Range Interactions Gergely Zimanyi, Ferenc Pazmandi We probe the droplet excitations in short range spin glasses by adding a perturbative long range interaction that decays with distance as a power law: $J/r^\sigma $. It is shown that if the power law exponent $\sigma $ is smaller than the spatial dimension $d$, the perturbation induces large scale avalanches which roll until they force the system to develop a pseudo gap in the excitation spectrum of the stabilities. This makes the perturbative long range interactions relevant for $\sigma <\sigma _c =d$. The droplet theory predicts that the critical exponent $\sigma _c $ depends on the droplet stiffness exponent as $\sigma _c =d-\theta .$ Combining these two results leads to a zero stiffness exponent $\theta =0$ in the droplet theory of short range spin glasses. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D14.00013: Introduction of a new thermodynamic property: ``characteristic frequency'' McKendree Pepper, Cristian Bahrim, Rafael Tadmor Fluctuations of thermodynamic properties are observed in the critical region of fluids, multiphase regions, and in systems containing a small number of molecules. We describe the dynamics within the vapor-liquid \textit{interfacial region} (IR) of a monatomic fluid in thermal equilibrium using fundamental principles of mechanics and thermodynamics. Our objective is to provide a new dynamic parameter which characterizes thermodynamic systems fluctuating near equilibrium, such as the IR. We call this new property \textit{``characteristic frequency''}. Our model assumes that the IR is (1) a closed thermodynamic system, (2) has a linear response to a driving force generated by a thermodynamic fluctuation, and (3) has a unique characteristic (resonant) frequency. We find that mild oscillations from equilibrium of a thermodynamic system occur at the most probable speed, and that the amplitude of the oscillations depends solely on the partition functions of the vapor and liquid within the IR. Our conclusion is that fluctuating thermodynamic systems at thermal equilibrium can exhibit oscillations analogous to mechanical systems and manifest a similar resonant response as the classical oscillators near their characteristic frequency. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D14.00014: An effective Fluctuation Theorem in Bidirectional Single-Electron Counting Yasuhiro Utsumi, Dimitry Golubev, Michael Marthaler, Keiji Saito, Toshimasa Fujisawa, Gerd Schoen We investigate the direction-resolved full counting statistics of single-electron tunneling through a double quantum dot system and compare with predictions of the fluctuation theorem (FT) for Markovian stochastic processes. Experimental data obtained for GaAs/GaAlAs heterostructures appear to violate the FT. After analyzing various potential sources for the discrepancy we conclude that the nonequilibrium shot noise of the measurement device influence the tunneling statistics. Taking these modifications into account we show how the FT can be violated due to measurement effects and recovered for fast detection by introducing an ``effective temperature.'' [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D14.00015: Landauer-Buettiker approach to current-induced forces in nanoelectromechanical systems Silvia Viola Kusminskiy, Niels Bode, Reinhold Egger, Felix von Oppen We study current-induced forces in nanoelectromechanical systems with coupling between electronic and mechanical degrees of freedom. We focus on the regime where the mechanical motion is slow and Coulomb blockade effects can be neglected. We derive the current-induced forces both in and out of equilibrium and give the conditions under which these forces can be expressed solely in terms of the S-matrix. We pay particular attention to situations with more than one mechanical degree of freedom which are characterized by several qualitatively new features. We apply our general results to some simple examples. [Preview Abstract] |
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