Lengthscale dependence of dynamic four-point susceptibilities in glass formers

TL;DR

This paper investigates how dynamic four-point susceptibilities in glass formers depend on length scales, using analytical models and simulations to support the universality of the dynamic facilitation scenario.

Contribution

It provides a detailed analysis of lengthscale dependence of four-point susceptibilities and confirms the dynamic facilitation approach as a generic description for glass-forming systems.

Findings

Susceptibilities depend on length scales as predicted by dynamic facilitation.

Analytical results are validated by simulations of atomistic and kinetically constrained models.

The dynamic facilitation scenario is shown to be a generic feature of glass formers.

Abstract

Dynamical four-point susceptibilities measure the extent of spatial correlations in the dynamics of glass forming systems. We show how these susceptibilities depend on the length scales that necessarily form part of their definition. The behaviour of these susceptibilities is estimated by means of an analysis in terms of renewal processes within the context of dynamic facilitation. The analytic results are confirmed by numerical simulations of an atomistic model glass-former, and of two kinetically constrained models. Hence we argue that the scenario predicted by the dynamic facilitation approach is generic.