Kovacs effect in facilitated spin models of strong and fragile glasses

TL;DR

This paper studies the Kovacs effect in facilitated spin models of glasses, revealing how the peak time dependence on temperature distinguishes relaxation mechanisms and showing similarities with real fragile glass formers.

Contribution

It demonstrates how the Kovacs peak time dependence can differentiate microscopic relaxation mechanisms in facilitated spin models of glasses.

Findings

Kovacs hump behavior is similar across models regardless of parameters.

Peak time dependence on temperature distinguishes relaxation mechanisms.

Facilitated spin models with d>1 and f>1 resemble fragile glass dynamics.

Abstract

We investigate the Kovacs (or crossover) effect in facilitated $f$-spin models of glassy dynamics. Although the Kovacs hump shows a behavior qualitatively similar for all cases we have examined (irrespective of the facilitation parameter $f$ and the spatial dimension $d$), we find that the dependence of the Kovacs peak time on the temperature of the second quench allows to distinguish among different microscopic mechanisms responsible for the glassy relaxation (e.g. cooperative vs defect diffusion). We also analyze the inherent structure dynamics underlying the Kovacs protocol, and find that the class of facilitated spin models with $d>1$ and $f>1$ shows features resembling those obtained recently in a realistic model of fragile glass forming liquid.