Anisotropic spatially heterogeneous dynamics in a model glass-forming binary mixture

TL;DR

This paper investigates the anisotropic nature of spatially heterogeneous dynamics in a model glass-forming binary mixture using four-point correlation functions, revealing strong anisotropy especially near the alpha relaxation time.

Contribution

It introduces the analysis of anisotropic four-point correlation functions in glass-forming liquids, highlighting their dependence on angle and time, which was not thoroughly explored before.

Findings

Four-point functions are anisotropic and angle-dependent.

Anisotropy is strongest for times longer than beta relaxation.

Strong anisotropy persists at low temperatures even for small wavevectors.

Abstract

We calculated a four-point correlation function G_4(k,r;t) and the corresponding structure factor S_4(k,q;t) for a model glass-forming binary mixture. These functions measure the spatial correlations of the relaxation of different particles. We found that these four-point functions are anisotropic and depend on the angle between vectors k and r (or q). The anisotropy is the strongest for times somewhat longer than the beta relaxation time but it is quite pronounced even for times comparable to the alpha relaxation time, tau_alpha. At the lowest temperatures S_4(k,q;tau_alpha) is strongly anisotropic even for the smallest wavevector q accessible in our simulation.