# Front-mediated melting of ultrastable glasses

## TL;DR

This study uses advanced simulations to observe and analyze the melting behavior of ultrastable glasses, revealing the dynamics of front and bulk melting and the influence of stability and deposition methods.

## Contribution

It provides the first direct simulation-based observation of both front and bulk melting in ultrastable glasses and measures the crossover length scale.

## Key findings

- Front melting velocity varies with conditions.
- Crossover length scale reaches nearly 400 particle diameters.
- Kinetic stability and vapor deposition influence melting behavior.

## Abstract

Ultrastable vapor-deposited glasses display uncommon material properties. Most remarkably, upon heating they are believed to melt via a liquid front that originates at the free surface and propagates over a mesoscopic crossover length, before crossing over to bulk melting. We combine swap Monte Carlo with molecular dynamics simulations to prepare and melt isotropic amorphous films of unprecedendtly high kinetic stability. We are able to directly observe both bulk and front melting, and the crossover between them. We measure the front velocity over a broad range of conditions, and a crossover length scale that grows to nearly $400$ particle diameters in the regime accessible to simulations. Our results disentangle the relative roles of kinetic stability and vapor deposition in the physical properties of stable glasses.