Glass formers display universal non-equilibrium dynamics on the level of single-particle jumps

¹ Physikalisches Institut, Albert-Ludwigs-Universität - Hermann-Herder-Str. 3, 79104 Freiburg, Germany
² Institut Charles Sadron, Université de Strasbourg, CNRS UPR22 - 23 rue du Loess, 67034 Strasbourg Cedex 2, France
³ Department of Physics and Astronomy, Bucknell University - Lewisburg, PA 17837, USA

Received: 21 October 2014
Accepted: 22 January 2015

Abstract

Glasses are inherently out-of-equilibrium systems evolving slowly toward their equilibrium state in a process called physical aging. During aging, dynamic observables depend on the history of the system, hampering comparative studies of dynamics in different glass formers. Here, we demonstrate how glass formers can be directly compared on the level of single-particle jumps, i.e. the structural relaxation events underlying the α-process. Describing the dynamics in terms of a continuous-time random walk, an analytic prediction for the jump rate is derived. The result is subsequently compared to molecular-dynamics simulations of amorphous silica and a polymer melt as two generic representatives of strong and fragile glass formers, and good agreement is found.