Two-step devitrification of ultrastable glasses

TL;DR

This study uses molecular dynamics simulations to reveal a two-step devitrification process in ultrastable glasses, showing how they transition into liquids with unique kinetics and large-scale domain formation.

Contribution

It provides the first microscopic analysis of devitrification in ultrastable glasses, highlighting a two-step process and deviations from classical kinetics.

Findings

Devitrification occurs after long times with a two-step process.

Isolated liquid droplets nucleate and grow slowly under pressure.

Large domains form after droplet coalescence, speeding up devitrification.

Abstract

The discovery of ultrastable glasses has raised novel challenges about glassy systems. Recent experiments studied the macroscopic devitrification of ultrastable glasses into liquids upon heating but lacked microscopic resolution. We use molecular dynamics simulations to analyse the kinetics of this transformation. In the most stable systems, devitrification occurs after a very large time, but the liquid emerges in two steps. At short times, we observe the rare nucleation and slow growth of isolated droplets containing a liquid maintained under pressure by the rigidity of the surrounding glass. At large times, pressure is released after the droplets coalesce into large domains, which accelerates devitrification. This two-step process produces pronounced deviations from the classical Avrami kinetics and explains the emergence of a giant lengthscale characterising the devitrification of bulk ultrastable glasses. Our study elucidates the nonequilibrium kinetics of glasses following a large temperature jump, which differs from both equilibrium relaxation and aging dynamics, and will guide future experimental studies.