Cage-jump motion reveals universal dynamics and non-universal structural features in glass forming liquids

TL;DR

This paper demonstrates that the distribution of particle diffusivities in glass-forming liquids becomes bimodal in the supercooled regime, revealing a universal dynamic phase coexistence linked to structural features, with implications for understanding glass transition.

Contribution

It introduces a method to identify dynamic phase coexistence via diffusivity distributions and links it to structural signatures, advancing the understanding of glass dynamics.

Findings

Diffusivity distribution becomes bimodal in supercooled regime

Structural bimodality correlates with dynamic phase coexistence

Different models show varying structural signatures

Abstract

The sluggish and heterogeneous dynamics of glass forming liquids is frequently associated to the transient coexistence of two phases of particles, respectively with an high and low mobility. In the absence of a dynamical order parameter that acquires a transient bimodal shape, these phases are commonly identified empirically, which makes difficult investigating their relation with the structural properties of the system. Here we show that the distribution of single particle diffusivities can be accessed within a Continuous Time Random Walk description of the intermittent motion, and that this distribution acquires a transient bimodal shape in the deeply supercooled regime, thus allowing for a clear identification of the two coexisting phase. In a simple two-dimensional glass forming model, the dynamic phase coexistence is accompanied by a striking structural counterpart: the distribution of the crystalline-like order parameter becomes also bimodal on cooling, with increasing overlap between ordered and immobile particles. This simple structural signature is absent in other models, such as the three-dimesional Kob-Andersen Lennard-Jones mixture, where more sophisticated order parameters might be relevant. In this perspective, the identification of the two dynamical coexisting phases opens the way to deeper investigations of structure-dynamics correlations.