Mapping dynamical heterogeneity in structural glasses to correlated fluctuations of the time variables

TL;DR

This paper investigates the origin of dynamical heterogeneities in structural glasses, providing evidence that soft time-reparametrization modes become dominant at lower temperatures, linking these fluctuations to glass transition phenomena.

Contribution

It introduces a method to decompose fluctuations into time-reparametrization and other components, supporting the hypothesis that soft modes underlie dynamical heterogeneity in glasses.

Findings

Time reparametrization fluctuations grow with decreasing temperature.

Correlation volumes of soft modes increase alongside dynamical heterogeneities.

Longitudinal fluctuations remain spatially localized across conditions.

Abstract

Dynamical heterogeneities -- strong fluctuations near the glass transition -- are believed to be crucial to explain much of the glass transition phenomenology. One possible hypothesis for their origin is that they emerge from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. To test this hypothesis, we use numerical simulation data from four glass-forming models to construct coarse grained observables that probe the dynamical heterogeneity, and decompose the fluctuations of these observables into two transverse components associated with the postulated time-fluctuation soft modes and a longitudinal component unrelated to them. We find that as temperature is lowered and timescales are increased, the time reparametrization fluctuations become increasingly dominant, and that their correlation volumes grow together with the correlation volumes of the dynamical heterogeneities, while the correlation volumes for longitudinal fluctuations remain small.