Dynamic particle tracking reveals the aging temperature of a colloidal glass

TL;DR

This study uses particle tracking to analyze the aging process of a colloidal glass, revealing that it thermalizes at a constant temperature higher than the bath, despite slow relaxation dynamics.

Contribution

It demonstrates that colloidal glasses exhibit thermalization at a constant temperature during aging, challenging the notion that aging systems cannot be characterized by an effective temperature.

Findings

Transport coefficients scale with aging time as a power-law.

The glass thermalizes at a temperature independent of age, higher than the bath.

Universal scaling law describes fluctuations of observables.

Abstract

Understanding glasses is considered to be one of the most fundamental problems in statistical physics. A theoretical approach to unravel their universal properties is to consider the validity of equilibrium concepts such as temperature and thermalization in these out-of-equilibrium systems. Here we investigate the autocorrelation and response function to monitor the aging of a colloidal glass. At equilibrium, all the observables are stationary while in the out-of-equilibrium glassy state they have an explicit dependence on the age of the system. We find that the transport coefficients scale with the aging-time as a power-law, a signature of the slow relaxation. Nevertheless, our analysis reveals that the glassy system has thermalized at a constant temperature independent of the age and larger than the bath, reflecting the structural rearrangements of cage-dynamics. Furthermore, a universal scaling law is found to describe the global and local fluctuations of the observables.