Non-monotonic temperature evolution of dynamic correlations in glass-forming liquids

TL;DR

This study uncovers a surprising non-monotonic change in spatial dynamical correlations in glass-forming liquids as temperature varies, revealing a new length scale and a qualitative shift in atomic motions near the mode-coupling temperature.

Contribution

The paper introduces a novel numerical method to detect and quantify spatial correlations, revealing a non-monotonic temperature evolution of dynamical correlations in glass-forming liquids.

Findings

Non-monotonic temperature dependence of spatial dynamical correlations.

Identification of a second, monotonically growing length scale.

A qualitative change in atomic motions near the mode-coupling temperature.

Abstract

The viscosity of glass-forming liquids increases by many orders of magnitude if their temperature is lowered by a mere factor of 2-3 [1,2]. Recent studies suggest that this widespread phenomenon is accompanied by spatially heterogeneous dynamics [3,4], and a growing dynamic correlation length quantifying the extent of correlated particle motion [5-7]. Here we use a novel numerical method to detect and quantify spatial correlations which reveal a surprising non-monotonic temperature evolution of spatial dynamical correlations, accompanied by a second length scale that grows monotonically and has a very different nature. Our results directly unveil a dramatic qualitative change in atomic motions near the mode-coupling crossover temperature [8] which involves no fitting or indirect theoretical interpretation. Our results impose severe new constraints on the theoretical description of the glass transition, and open several research perspectives, in particular for experiments, to confirm and quantify our observations in real materials.