String-like Rearrangements Induce Mobility in Supercooled Liquids

TL;DR

This paper shows that in supercooled liquids, local string-like rearrangements called microstrings facilitate mobility by propagating relaxation events, confirming the role of dynamical facilitation in heterogeneity.

Contribution

It provides evidence that string-like rearrangements are the primary mechanism for mobility propagation, supporting the dynamical facilitation theory.

Findings

Dynamical heterogeneity results from local relaxation events.

Mobility propagates via microstrings, not structural perturbations.

Spatiotemporal correlations confirm facilitation as key mechanism.

Abstract

Dynamical heterogeneity is a signature phenomenon of deeply supercooled liquids and glasses. Here, we demonstrate that the spatiotemporal correlations between local relaxation events that underpin it are the result of local relaxation events raising the likelihood that other relaxation events subsequently occur nearby, confirming a widely held, but until now unsubstantiated, belief that dynamical facilitation is responsible for dynamical heterogeneity. We find that mobility is propagated through the entrainment of particles into elementary string-like rearrangements, known as microstrings, and not through perturbing the structure surrounding these rearrangements.