Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R3: Invited Session: Nonequilibrium Relaxation and Aging in Materials |
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Sponsoring Units: GSNP DCMP Chair: Uew Tauber, Virginia Polytechnical Institute and State University Room: Ballroom III |
Wednesday, March 20, 2013 2:30PM - 3:06PM |
R3.00001: Nonequilibrium behavior in strongly correlated electron systems Invited Speaker: Dragana Popovi\'c There is growing evidence that nonequilibrium behavior may underlie many complex phenomena exhibited by strongly correlated electronic materials with disorder. A two-dimensional electron system (2DES) in Si metal-oxide-semiconductor field-effect transistors has emerged as an excellent model system for studying glassy or nonequilibrium charge dynamics near the metal-insulator transition (MIT). In particular, studies of both conductance relaxations and noise on disordered samples, using several different experimental protocols, have established that the 2DES in Si exhibits all the main manifestations of glassiness: slow, correlated dynamics, nonexponential relaxations, diverging equilibration time (as temperature $T\rightarrow 0$), aging and memory. The results provide strong evidence that many such universal features are robust manifestations of glassiness, regardless of the dimensionality of the system. In addition, the experiments show that the 2D MIT is closely related to the melting of this Coulomb glass. The observations are consistent with predictions of the theoretical models that describe the MIT as a Mott transition with disorder. Some effects that are unique to Coulomb glasses have also been revealed, which should have important implications for theoretical modeling of the glassy dynamics in a 2DES and other strongly correlated materials. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:42PM |
R3.00002: Universally slow Invited Speaker: Ariel Amir Glassy systems are very common in nature, from disordered electronic and magnetic systems to window glasses and crumpled paper. Among their key properties are slow relaxations to equilibrium without a typical timescale, and dependence of relaxation on the system's age. After reviewing some of these physical systems, I will describe our approach to the problem, and show how it leads to a novel class of aging. The slow relaxations result from a broad distribution of ``relaxation eigenmodes,'' which relates to a particular class of random matrices. I will discuss recent results on the structure and localization properties of these modes, and their implications. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 4:18PM |
R3.00003: Dynamical symmetries in ageing phenomena Invited Speaker: Malte Henkel Systems undergoing physical ageing can be characterised by (i) undergoing slow relaxation (ii) absence of time-translation-invariance and (iii) dynamical scaling. Specific examples are obtained by quenching many-body systems from a high-temperature initial state to below their critical temperature. Here, we shall consider consequences of an assumed extension of dynamical scaling to a larger group of {\em local scale-transformations}. Explicit scaling forms of two-time responses and correlators are obtained. These will be compared with simulational data in simple magnets, as well as in many-body systems without an equilibrium stationary state, such as critical directed percolation or domain-growth in the Kardar-Parisi-Zhang universality class.\\[4pt] [1] M. Henkel, M. Pleimling, {\it Non-equilibrium phase transitions}, Vol. 2, Springer (Heidelberg 2010) \\[0pt] [2] M. Henkel, J.D. Noh, M. Pleimling, Phys. Rev. {\bf E85}, 030102(R) (2012) {\tt [arxiv:1109.5022]} \\[0pt] [3] M. Henkel, {\tt arxiv:1009.4139} \\[0pt] [4] M. Henkel, S. Stoimenov, Nucl. Phys. {\bf B847} [FS], 612 (2011) {\tt [arxiv:1011.6315]} [Preview Abstract] |
Wednesday, March 20, 2013 4:18PM - 4:54PM |
R3.00004: Probing equilibrium by nonequilibrium dynamics: Aging in Co/Cr superlattices Invited Speaker: Christian Binek Magnetic aging phenomena are investigated in a structurally ordered Co/Cr superlattice through measurements of magnetization relaxation, magnetic susceptibility, and hysteresis at various temperatures above and below the onset of collective magnetic order. We take advantage of the fact that controlled growth of magnetic multilayer thin films via molecular beam epitaxy allows tailoring the intra and inter-layer exchange interaction and thus enables tuning of magnetic properties including the spin-fluctuation spectra. Tailored nanoscale periodicity in Co/Cr multilayers creates mesoscopic spatial magnetic correlations with slow relaxation dynamics when quenching the system into a nonequilibrium state. Magnetization relaxation in weakly correlated spin systems depends on the microscopic spin-flip time of about 10 ns and is therefore a fast process. The spin correlations in our Co/Cr superlattice bring the magnetization dynamics to experimentally better accessible time scales of seconds or hours. In contrast to spin-glasses, where slow dynamics due to disorder and frustration is a well-known phenomenon, we tune and increase relaxation times in ordered structures. This is achieved by increasing spin-spin correlation between mesoscopically correlated regions rather than individual atomic spins, a concept with some similarity to block spin renormalization. Magnetization transients are measured after exposing the Co/Cr heterostructure to a magnetic set field for various waiting times. Scaling analysis reveals an asymptotic power-law behavior in accordance with a full aging scenario. The temperature dependence of the relaxation exponent shows pronounced anomalies at the equilibrium phase transitions of the antiferromagnetic superstructure and the ferromagnetic to paramagnetic transition of the Co layers. The latter leaves only weak fingerprints in the equilibrium magnetic behavior but gives rise to a prominent change in nonequilibrium properties. Our findings suggest that scaling analysis of nonequilibrium data can serve as a probe for weak equilibrium phase transitions. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:30PM |
R3.00005: Aging processes in disordered materials: High-$T_c$ superconductors and ferromagnets Invited Speaker: Michel Pleimling Physical aging is generically encountered in systems far from equilibrium that evolve with slow dynamics. Well known examples can be found in structural glasses, spin glasses, magnetic systems, and colloids. Recent years have seen major breakthroughs in our understanding of aging processes in non-disordered systems. Progress in understanding aging in disordered systems has been much slower though. In this talk I discuss non-equilibrium relaxation in two different types of disordered systems: coarsening ferromagnets with disorder, characterized by a crossover from an initial power-law like growth of domains to a slower logarithmic growth regime, and interacting vortex lines in disordered type-II superconductors, where the interplay of vortex-vortex interaction and pinning results in a very rich non-equilibrium behavior. [Preview Abstract] |
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