The Kovacs effect in model glasses

TL;DR

This paper analyzes the Kovacs memory effect in glassy systems, using theoretical models to understand its origin and shape, highlighting the role of heterogeneity and suggesting ways to interpret experimental data.

Contribution

It provides a detailed analytical study of the Kovacs effect using domain growth and traps models, linking the phenomenon to system heterogeneity and offering insights for experimental analysis.

Findings

Kovacs effect arises from system heterogeneity.

Shape of the Kovacs hump can be predicted by models.

Heterogeneity requires full probability distribution analysis.

Abstract

We discuss the `memory effect' discovered in the 60's by Kovacs in temperature shift experiments on glassy polymers, where the volume (or energy) displays a non monotonous time behaviour. This effect is generic and is observed on a variety of different glassy systems (including granular materials). The aim of this paper is to discuss whether some microscopic information can be extracted from a quantitative analysis of the `Kovacs hump'. We study analytically two families of theoretical models: domain growth and traps, for which detailed predictions of the shape of the hump can be obtained. Qualitatively, the Kovacs effect reflects the heterogeneity of the system: its description requires to deal not only with averages but with a full probability distribution (of domain sizes or of relaxation times). We end by some suggestions for a quantitative analysis of experimental results.