Activated aging dynamics and negative fluctuation-dissipation ratios

TL;DR

This paper investigates how thermal activation during aging in glassy materials can cause negative response functions and violations of the fluctuation-dissipation theorem, supported by theoretical and numerical analysis of kinetically constrained models.

Contribution

It introduces the concept of negative fluctuation-dissipation ratios arising from activated aging, providing a new perspective on glassy dynamics.

Findings

Negative fluctuation-dissipation ratios observed in models

Theoretical and numerical evidence for violations of fluctuation-dissipation theorem

Relevance to aging in glass-formers and granular materials

Abstract

In glassy materials aging proceeds at large times via thermal activation. We show that this can lead to negative dynamical response functions and novel and well-defined violations of the fluctuation-dissipation theorem, in particular, negative fluctuation-dissipation ratios. Our analysis is based on detailed theoretical and numerical results for the activated aging regime of simple kinetically constrained models. The results are relevant to a variety of physical situations such as aging in glass-formers, thermally activated domain growth and granular compaction.