Aging in thermal active glasses

TL;DR

This study investigates how active thermal glasses age differently from passive glasses, revealing unique aging dynamics characterized by evolving effective temperatures and constant heterogeneity, challenging previous assumptions about active-passive system equivalence.

Contribution

It provides the first detailed numerical comparison of aging in active versus passive thermal glasses, highlighting fundamental differences in their aging mechanisms.

Findings

Active glasses exhibit a time-dependent effective temperature during aging.

Dynamic heterogeneity remains small and constant in active aging systems.

Active and passive glasses do not map onto each other through a simple effective temperature.

Abstract

It is well established that glassy materials can undergo aging, i.e., their properties gradually change over time. There is rapidly growing evidence that dense active and living systems also exhibit many features of glassy behavior, but it is still largely unknown how physical aging is manifested in such active glassy materials. Our goal is to explore whether active and passive thermal glasses age in fundamentally different ways. To address this, we numerically study the aging dynamics following a quench from high to low temperature for two-dimensional passive and active Brownian model glass-formers. We find that aging in active thermal glasses is governed by a time-dependent competition between thermal and active effects, with an effective temperature that explicitly evolves with the age of the material. Moreover, unlike passive aging phenomenology, we find that the degree of dynamic heterogeneity in active aging systems is relatively small and remarkably constant with age. We conclude that the often-invoked mapping between an active system and a passive one with a higher effective temperature rigorously breaks down upon aging, and that the aging dynamics of thermal active glasses differs in several distinct ways from both the passive and athermal active case.