Statistical Physics and Condensed Matter

Glassy Dynamics

Heinz Horner, Reimer Kühn, W. Zippold

Introduction

Relaxtion times in spin-glasses or glasses are observed to grow to such an extent at low temperatures that these systems do not reach thermal equilibrium on experimentally accessible time-scales. Properties of such systems are then often found to depend on their history of preparation; such systems are said to age. Similar observations are made in coarsening dynamics at first order phase transitions. Some properties of spin-glasses and glasses must therefore be studied via dynamical approaches which allow taking possible history dependence explicitly into account. Fluctuation dissipation theorems which connect correlation and response functions in thermal equilibrium are found to be broken in aging systems. We are studying simple models of spin-glasses in order to understand, in particular, their dynamics on long time scales. Some of these models exhibit dynamical freezing transitions without undergoing a thermodynamic phase transition. It is believed that such a scenario is occurring also in the much less well-understood case of the glass-transition in structural glasses.

Recent Papers

Non-Equilibrium Dynamics of Simple Spherical Spin Models
by W. Zippold, R. Kühn and H. Horner
Eur. Phys. J. B. 13, 531-537 (1999) (gzipped ps).
We investigate the non-equilibrium dynamics of spherical spin models with two-spin interactions. For the exactly solvable models of the d-dimensional spherical ferromagnet and the spherical Sherrington-Kirkpatrick (SK) model the asymptotic dynamics has for large times and large waiting times the same formal structure. In the limit of large waiting times we find in both models an intermediate time scale, scaling as a power of the waiting time with an exponent smaller than one, and thus separating the time-translation-invariant short-time dynamics from the aging regime. It is this time scale on which the fluctuation-dissipation theorem is violated. Aging in these models is similar to that observed in spin glasses at the level of correlation functions, but different at the level of response functions, and thus different at the level of experimentally accessible quantities like thermoremanent magnetization.

.... under construction; more items to be added

kuehn@tphys.uni-heidelberg.de 17.10.1999