Mean-field description for the architecture of low-energy excitations in glasses

TL;DR

This paper develops a mean-field scaling theory for the geometry and energy of low-energy excitations in glasses, explaining their behavior near instabilities and how they change with cooling.

Contribution

It introduces a novel mean-field based scaling description for low-energy excitations in glasses, connecting their properties to the proximity of an instability.

Findings

Excitations become less extended with cooling.

Energy and displacement scales increase upon cooling.

The theory matches observations in ultrastable computer glasses.

Abstract

In amorphous materials, groups of particles can rearrange locally into a new stable configuration. Such elementary excitations are key as they determine the response to external stresses, as well as to thermal and quantum fluctuations. Yet, understanding what controls their geometry remains a challenge. Here we build a scaling description of the geometry and energy of low-energy excitations in terms of the distance to an instability, as predicted for instance at the dynamical transition in mean field approaches of supercooled liquids. We successfully test our predictions in ultrastable computer glasses, with a gapped and ungapped (regular) spectrum. Overall, our approach explains why excitations become less extended, with a higher energy and displacement scale upon cooling.