Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session L2: Systems Far from Equilibrium |
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Chair: Michel Pleimling, Virginia Tech University Room: Salon C |
Saturday, November 12, 2016 8:30AM - 9:00AM |
L2.00001: Record Dynamics: Direct Experimental Evidence from Jammed Colloids Invited Speaker: Stefan Boettcher In a broad class of complex materials a quench leads to a multi-scaled relaxation process known as aging. To explain its commonality and the astounding insensitivity to most microscopic details, record dynamics (RD) posits that a sub-extensive set of irreversible events, so called quakes, controls the dynamics. While key predictions of RD are known to concur with a number of experimental and simulational results, its basic assumption on the nature of quake statistics has proven extremely difficult to verify experimentally. The careful distinction of rare (”record”) cage-breaking events from in-cage rattle accomplished in previous experiments on jammed colloids [PRL103(2009)115701] enables us to extract the first direct experimental evidence for the fundamental hypothesis of RD that the rate of quake events decelerates with the inverse of the system age. The resulting description shows the predicted growth of the particle mean-square displacement and of a mesoscopic length-scale with the logarithm of time. [Preview Abstract] |
Saturday, November 12, 2016 9:00AM - 9:30AM |
L2.00002: Non-equilibrium Relaxation of Driven Topological Defects Invited Speaker: Uwe C. Tauber The non-equilibrium relaxation kinetics of topological defects in condensed matter systems provides a novel diagnostic tool to probe their fluctuation spectrum and dynamical correlations. We study the effects of rapid temperature, magnetic field, and driving current changes on the non-equilibrium relaxation dynamics of magnetic vortex lines in disordered type-II superconductors by employing a three-dimensional elastic line model and performing Langevin molecular dynamics simulations. We utilize the current-voltage characteristics, mean vortex radius of gyration and the fraction of pinned line elements as well as two-time flux line height autocorrelations and their mean-square displacement to study the non-linear stochastic relaxation kinetics in the physical aging regime. This allows us to distinguish the complex relaxation features that result from either point-like or columnar pinning centers and reflect the intricate competition between vortex pinning, line elasticity, and mutual repulsive interactions. With similar numerical tools, we investigate the dynamics of driven skyrmion topological defects in ferromagnetic thin films subject to the prominent Magnus force. References: [1] H. Assi, H. Chaturvedi, U. Dobramysl, M. Pleimling, and U.C. T\"auber, Phys. Rev. E {\bf 92}, 052124 (2015) [{\tt arXiv: 1505.06240}]; [2] H. Assi, H. Chaturvedi, U. Dobramysl, M. Pleimling, and U.C. T\"auber, Mol. Simul. (in print, 2016) [{\tt arXiv:1509.02227}]; [3] H. Chaturvedi, H. Assi, U. Dobramysl, M. Pleimling, and U.C. T\"auber, J. Stat. Mech. (in print, 2016) [{\tt arXiv:1606.06100}]. [Preview Abstract] |
Saturday, November 12, 2016 9:30AM - 10:00AM |
L2.00003: Metastability and Instability in a Model Spin-crossover Material: Free-energy Landscapes Explored by a Constrained Wang-Landau Monte Carlo Method Invited Speaker: Per Arne Rikvold Spin-crossover materials present an interesting example of systems with competing interactions on different length scales. Here I present a “toy model” of such a system: a square-lattice Ising model with nearest-neighbor antiferromagnetic and mean-field like long-range ferromagnetic interactions. Using standard importance sampling Monte Carlo (MC) methods, we have recently obtained rather complex phase diagrams for this model in several parameter regimes [PAR, G. Brown, S. Miyashita, C. Omand, M. Nishino, PRB 93, 064109 (2016)]. One question that cannot easily be answered by these methods, is that of the structure of the free-energy landscape in the space of the two macroscopic order parameters: magnetization and staggered magnetization. We have therefore developed a new method to directly obtain the density of states (DOS) of such a model, using the Wang-Landau MC (WLMC) method. I will briefly discuss our modifications to the original WLMC method to obtain DOS constrained to specific values of the two order parameters, and show the resulting numerical free-energy landscapes and phase diagrams for several parameter values [C.-H. Chan, G. Brown, PAR, unpublished]. Comparison with phase diagrams by standard MC raises some new questions about the nature of metastable phases in models with competing short- and long-range interactions. [Preview Abstract] |
Saturday, November 12, 2016 10:00AM - 10:30AM |
L2.00004: Noise-induced transitions in bistable electronic systems Invited Speaker: Stephen Teitsworth Bistable systems occur throughout the natural sciences and when such systems are subjected to random noise, one observes probabilistic transitions between co-existing metastable states. Such behavior is found in chemical reaction kinetics, driven nonlinear mechanical systems, nonlinear electronic transport systems, climate variability models, and pulse propagation dynamics in neurons, to name but a few. In this talk, I will discuss recent work carried out in my group on noise-induced transitions in bistable systems that are far from thermal equilibrium. Experimental studies focus on switching transitions between distinct states of electrical current flow in quantum tunneling structures such as semiconductor superlattices and tunnel diodes. [Preview Abstract] |
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