Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A17: Focus Session: Strong Correlations in Systems Far from Equilibrium I |
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Sponsoring Units: GSNP Chair: Michel Pleimling, Virginia Polytechnic Institute and State University Room: 402 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A17.00001: Localization Protected Quantum Order Rahul Nandkishore, David Huse, Shivaji Sondhi, Vadim Oganesyan, Arijeet Pal Closed quantum systems with quenched randomness exhibit many-body localized regimes wherein they do not equilibrate even though prepared with macroscopic amounts of energy above their ground states. We show that such localized systems can order in that individual many-body eigenstates can break symmetries or display topological order in the infinite volume limit. Indeed, isolated localized quantum systems can order even at energy densities where the corresponding thermally equilibrated system is disordered, i.e.: localization protects order. In addition, localized systems can move between ordered and disordered localized phases via non-thermodynamic transitions in the properties of the many-body eigenstates. We give evidence that such transitions may proceed via localized critical points. We note that localization provides protection against decoherence that may allow experimental manipulation of macroscopic quantum states. We also identify a `spectral transition' involving a sharp change in the spectral statistics of the many-body Hamiltonian. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A17.00002: Many-body Localization and Symmetry Protected Topological Order Vedika Khemani, Anushya Chandran, C.R. Laumann, S.L. Sondhi Recent work shows that highly excited many-body localized eigenstates can exhibit broken symmetries and topological order, including in dimensions where such order would be forbidden in equilibrium. We extend this analysis to discrete symmetry protected order via the explicit examples of the Haldane phase of one dimensional spin chains and the topological Ising paramagnet in two dimensions. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A17.00003: Signatures of electron-magnon interaction in charge and spin current in magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach Farzad Mahfouzi, Branislav Nikolic We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the perturbation expansion for the electron and magnon self-energies of the nonequilibrium Green function (NEGF) formalism applied to electron-magnon (e-m) interacting system driven out of equilibrium by finite bias voltage. This is then employed to understand the effect of inelastic e-m scattering on current-voltage ({\em I--V)} characteristics of F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs). For this purpose, we evaluate self-consistently Fock diagram for the electron self-energy which ensures charge current conservation (i.e., sum of charge currents in all leads must be zero), as well as electron-hole polarization bubble diagram for magnon self-energy, where respective GF lines within these diagrams are the fully interacting ones. Furthermore we present the formulation to calculate the Fano factor in correlated systems out of equilibrium and then investigate the effect of e-m coupling on noise in MTJs. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A17.00004: Propagation of wave pakets in 1d spin systems - ballistic, diffusive, many-body localized? Christoph Karrasch, Fabian Heidrich-Meisner, Jens Bardarson, Frank Pollmann, Joel Moore We study the propagation of local spin wave pakets in one-dimensional XXZ spin chains in presence of disorder. We employ a time-dependent finite-temperature density matrix renormalization group algorithm. For clean chains, the spin density spreads ballistically in the Luttinger liquid phase and diffusively in the gapped phase. We investigate the interplay of interactions and disorder and discuss how (and if) metallic and many-body localized phases manifest in this setup. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A17.00005: Double-pulse deexcitations in a one-dimensional strongly correlated system Takami Tohyama, Hantao Lu, Janez Bonca We investigate the ultrafast optical response of the one-dimensional half-filled extended Hubbard model exposed to two successive laser pulses [1]. By using the time-dependent Lanczos method, we find that following the first pulse, the excitation and deexcitation process between the ground state and excitonic states can be precisely controlled by the relative temporaldisplacement of the pulses. The underlying physics can be understood in terms of a modified Rabi model. Our simulations clearly demonstrate the controllability of ultrafast transition between excited and deexcited phases in strongly correlated electron systems.\\[4pt] [1] H. Lu, J. Bonca, and T. Tohyama, EPL {\bf 103}, 57005 (2013). [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A17.00006: Driven-dissipative Bose-Einstein condensation: perturbative field-theoretic renormalization group approach Sebastian Diehl, Uwe C. Tauber The universal critical behavior of the driven-dissipative non-equilibrium Bose condensation transition is investigated employing the field-theoretic renormalization group method. Such criticality may be realized in broad ranges of driven open systems on the interface of quantum optics and many-body physics, from exciton-polariton condensates to cold atomic gases. The starting point is a noisy and dissipative Gross-Pitaevski equation corresponding to a complex valued Landau-Ginzburg functional, which captures the near critical non-equilibrium dynamics, and generalizes Model A for classical relaxational dynamics with non-conserved order parameter. We confirm and further develop the physical picture previously established by means of a functional renormalization group study of this system. Complementing this earlier numerical analysis, we analytically compute the static and dynamical critical exponents at the condensation transition to lowest non-trivial order in the dimensional $\epsilon$ expansion about the upper critical dimension $d_c = 4$, and establish the emergence of a novel universal scaling exponent associated with the non-equilibrium drive. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:48AM |
A17.00007: Exciton reactions on carbon nanotubes: an experimental testbed for critical dynamics Invited Speaker: Jeremy Allam The one-dimensional coalescing random walk ($X+X\to X)$ is a paradigmatic reaction-diffusion system due to both its exact solvability [1,2] and the experimental observation of nonclassical kinetics at asymptotically long times [3]. The solvability rests on the anticommutative property of intersecting trajectories of particles that react \textit{instantly} and at \textit{short range}: however, the validity of these assumptions in real systems has not previously been tested by experiment. We have shown that exciton-exciton recombination (fusion) on carbon nanotubes provides a platform for quantitative studies of critical kinetics in a simple non-equilibrium system [4]. Under high excitation density we observed a crossover in the exciton density $n$ between regimes of classical $(n\propto t^{-1})$ and anomalous $(n\propto t^{-1/2})$ scale invariance as predicted by renormalization group [5] and approximate [1] theories, arising from a finite reaction probability of $\approx 0.2$ per encounter. At long times the exciton population per nanotube exponentially approaches unity (i.e. a finite size effect), allowing calibration of the exciton density and hence a demonstration of universality extending over both classical and critical regimes. Under low excitation, the early kinetics followed a Smoluchowski-Noyes form ${dn} \mathord{\left/ {\vphantom {{dn} {dt}}} \right. \kern-\nulldelimiterspace} {dt}\propto n^{2}t^{-1/2}$ rather than the asymptotic ${dn} \mathord{\left/ {\vphantom {{dn} {dt}}} \right. \kern-\nulldelimiterspace} {dt}\propto n^{3}$, providing direct evidence for the spatial self-ordering that precedes critical scale invariance. We studied the re-emergence of microscopic detail at the classical-nonclassical crossover, which is abrupt and nonmonotonic due to competition between temporal and spatial averaging of critical fluctuations (i.e. finite reaction rate and range). It appears that real-world experiments will require more complete descriptions of the interactions than is available in existing models.\\[4pt] [1] D. Ben-Avraham and S. Havlin, \textit{Diffusion and Reactions in Fractals and Disordered Systems} (Cambridge University Press, Cambridge, 2000).\\[0pt] [2] G. M. Sch\"{u}tz, Phase Transitions and Critical Phenomena 19, 1 (2001).\\[0pt] [3] J. Prasad and R. Kopelman, Phys. Rev. Lett. 59, 2103 (1987).\\[0pt] [4] J. Allam et al., Phys. Rev. Lett. 111, 197401 (2013).\\[0pt] [5] U. C. T\"{a}uber et al., \textit{J. Phys. A: Math. Gen.} 38, R79--R131 (2005). [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A17.00008: On local temperatures near absolute zero in nonequilibrium quantum systems Abhay Shastry, Justin Bergfield, Charles Stafford The local temperature of a quantum conductor with source at finite temperature and drain at or near absolute zero is investigated, a problem outside the scope of linear response theory. The local temperature is defined by the measurement of a floating thermoelectric probe. It is shown that cold spots with local temperatures near absolute zero exist within the system, and the applicability of the third law of thermodynamics is investigated. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A17.00009: Critical exponents describing non-stationary $1/f$ noise for intermittent quantum dots Sanaz Sadegh, Eli Barkai, Diego Krapf Semiconductor quantum dots (QDs) exhibit bright fluorescence, but this emission switches randomly between ``on'' and ``off'' states that are distributed according to universal power laws. This scale-free dynamics is responsible for weak ergodicity breaking and non-stationarity. Such stochastic processes yield a power spectrum of the form $S(f)=A/f^{\beta}$. Power spectrum analysis is a superior method for studying the properties of QD emission because it does not depend on the arbitrary determination of a threshold, typically used in the discrimination between ``on'' and ``off'' states. Recently, intriguing predictions have been made about the power spectrum aging properties and the role of finite measurement time. To test these predictions, we study the emission power spectra from 1200 QDs at room temperature. We find that five exponents are needed to describe the power spectrum properties, namely spectral exponent, power spectrum aging, cutoff frequency, zero frequency spectrum, and total power. We also compare our results with numerical simulations and explain observed discrepancies based on the combined action of Gaussian noise and the truncation of the ``on''-time distribution. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A17.00010: Many-body localization in the quantum random energy model Chris Laumann, Arijeet Pal The quantum random energy model is a canonical toy model for a quantum spin glass with a well known phase diagram. We show that the model exhibits a many-body localization-delocalization transition at finite energy density which significantly alters the interpretation of the statistical ``frozen'' phase at lower temperature in isolated quantum systems. The transition manifests in many-body level statistics as well as the long time dynamics of on-site observables. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A17.00011: The effects of magnetic field and temperature quenches on non-equilibrium relaxation properties of vortex lines in type-II superconductors Hiba Assi, Ulrich Dobramysl, Michel Pleimling, Uwe T\"{a}uber Technological applications of type-II superconductors require a deep understanding of the dynamics of vortex matter in these complex materials. We model vortices in the London limit as interacting elastic lines, and simulate their dynamics employing a Langevin molecular dynamics (LMD) algorithm. This LMD algorithm is utilized to investigate the non-equilibrium relaxation properties of interacting lines, subject to randomly-placed point or correlated columnar pinning sites, by studying various two-time correlation functions. We consider experimentally-motivated initial conditions by applying quenches in the system temperature or the magnetic field, which is realized by suddenly adding or removing vortex lines from the system. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A17.00012: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 10:48AM - 11:00AM |
A17.00013: A General Model for Brownian Vortexes Henrique Moyses, Ross Bauer, David Grier Brownian Vortexes are a class of non-equilibrium steady states that arise from the motion of Brownian particles in non-conservative force fields. At non-zero temperature the non-conservative part of the force bias the particles' fluctuations into probability currents, which due to the conservation of probability should feature closed loops. Previous studies have shown that Brownian Vortexes comprise a distinct class of stochastic processes whose direction and topology of the developed flux can be tuned by changing the temperature of the system. Here we present a general model for Brownian Vortexes that is based on a perturbation theory scheme of the Fokker - Planck equation to get the probability distribution and non-equilibrium steady state flux of such system. This generalized model features the temperature induced probability flux reversal and topological changes characteristic of this stochastic system in the case where the non-conservative part of the force is small compared to the conservative one. We further compare the theoretically predicted results with numerical simulations and propose an experimental test system based on the motion of colloidal particles in optical traps. [Preview Abstract] |
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