Revisiting the Concept of Activation in Supercooled Liquids

TL;DR

This paper reevaluates the dynamics of supercooled liquids, showing that activation is driven by entropy rather than energy barriers, and challenges the traditional trap-based activated dynamics picture.

Contribution

It introduces a new perspective that activation in supercooled liquids is primarily entropic, not energetic, and provides measures linking glassiness onset to the landscape.

Findings

Metabasin waiting times are extremely broad, exceeding relaxation times.

Activation is driven by entropic barriers, not energetic traps.

Standard trap models do not fully explain the dynamics in this regime.

Abstract

In this work we revisit the description of dynamics based on the concepts of metabasins and activation in mildly supercooled liquids via the analysis of the dynamics of a paradigmatic glass former between its onset temperature $T_{o}$ and mode-coupling temperature $T_{c}$. First, we provide measures that demonstrate that the onset of glassiness is indeed connected to the landscape, and that metabasin waiting time distributions are so broad that the system can remain stuck in a metabasin for times that exceed $\tau_\alpha$ by orders of magnitude. We then reanalyze the transitions between metabasins, providing several indications that the standard picture of activated dynamics in terms of traps does not hold in this regime. Instead, we propose that here activation is principally driven by entropic instead of energetic barriers. In particular, we illustrate that activation is not controlled by the hopping of high energetic barriers, and should more properly be interpreted as the entropic selection of nearly barrierless but rare pathways connecting metabasins on the landscape.