Front propagation versus bulk relaxation in the annealing dynamics of a kinetically constrained model of ultrastable glasses

TL;DR

This paper uses a kinetically constrained model to simulate ultrastable glass annealing, revealing a competition between front propagation and bulk relaxation that explains experimental observations of stability and film thickness effects.

Contribution

It introduces a three-dimensional East model with soft constraints to reproduce ultrastable glass annealing dynamics, highlighting the interplay of different relaxation mechanisms.

Findings

Front propagation dominates in thin films.

Bulk relaxation becomes significant in thicker films.

Model reproduces experimental annealing behavior.

Abstract

Glasses prepared by physical vapour deposition have been shown to be remarkably more stable than those prepared by standard cooling protocols, with properties that appear to be similar to systems aged for extremely long times. When subjected to a rapid rise in temperature, ultrastable glasses anneal towards the liquid in a qualitatively different manner than ordinary glasses, with the seeming competition of different timescales and lengthscales. We numerically reproduce the phenomenology of ultrastable glass annealing with a kinetically constrained model, a three dimensional East model with soft constraints, in a setting where the bulk is in an ultrastable configuration and a free surface is permanently excited. Annealing towards the liquid state is given by the competition between the ballistic propagation of a front from the free surface and a much slower nucleation-like relaxation in the bulk. The crossover between these mechanisms also explains the change in behaviour with film thickness seen experimentally.