Subdiffusion and intermittent dynamic fluctuations in the aging regime of concentrated hard spheres

TL;DR

This paper investigates the aging dynamics of concentrated hard spheres, revealing subdiffusive particle motion, intermittent relaxation events, and localized dynamic fluctuations during the aging process.

Contribution

It provides new insights into the aging regime of dense particle systems, highlighting subdiffusive behavior and localized relaxation events through computer simulations.

Findings

Relaxation time increases exponentially then linearly with age.

Particle displacements are broad and non-Gaussian, indicating non-Fickian diffusion.

Relaxation events are temporally intermittent and spatially localized.

Abstract

We study the nonequilibrium aging dynamics in a system of quasi-hard spheres at large density by means of computer simulations. We find that, after a sudden quench to large density, the relaxation time initially increases exponentially with the age of the system. After a surprisingly large crossover time, the system enters the asymptotic aging regime characterized by a linear increase of the relaxation time with age. In this aging regime, single particle motion is strongly non-Fickian, with a mean-squared displacement increasing subdiffusively, associated to broad, non-Gaussian tails in the distribution of particle displacements. We find that the system ages through temporally intermittent relaxation events, and a detailed finite size analysis of these collective dynamic fluctuations reveals that these events are not spanning the entire system, but remain spatially localized.