Manifestations of Dynamical Facilitation in Glassy Materials

TL;DR

This paper investigates how dynamical facilitation manifests in glassy materials using lattice models, revealing that facilitation remains significant across different conditions and challenging recent claims about its diminishing role.

Contribution

It introduces new measures for dynamical facilitation and demonstrates its persistent importance in glassy dynamics, countering recent experimental claims.

Findings

Avalanches occur in kinetically constrained models.

Decreasing avalanche size with supercooling does not mean facilitation diminishes.

Dynamical facilitation remains significant across various state points.

Abstract

By characterizing the dynamics of idealized lattice models with a tunable kinetic constraint, we explore the different ways in which dynamical facilitation manifests itself within the local dynamics of glassy materials. Dynamical facilitation is characterized both by a mobility transfer function, the propensity for highly-mobile regions to arise near regions that were previously mobile, and by a facilitation volume, the effect of an initial dynamical event on subsequent dynamics within a region surrounding it. Sustained bursts of dynamical activity -- avalanches -- are shown to occur in kinetically constrained models, but, contrary to recent claims, we find that the decreasing spatiotemporal extent of avalanches with increased supercooling previously observed in granular experiments does not imply diminishing facilitation. Viewed within the context of existing simulation and experimental evidence, our findings show that dynamical facilitation plays a significant role in the dynamics of systems investigated over the range of state points accessible to molecular simulations and granular experiments.