Thermodynamic signature of growing amorphous order in glass-forming liquids

TL;DR

This paper uncovers a thermodynamic signature of growing amorphous order in glass-forming liquids, showing boundary influence propagates over larger scales as temperature decreases, challenging existing theories.

Contribution

It provides the first thermodynamic evidence of increasing static correlation lengths in supercooled liquids and suggests a need to generalize RFOT theory to include fluctuating surface tension.

Findings

Boundary influence propagates over larger lengthscales upon cooling.

Static correlation length grows and decays nonexponentially.

Results challenge standard RFOT assumptions.

Abstract

Although several theories relate the steep slowdown of glass formers to increasing spatial correlations of some sort, standard static correlation functions show no evidence for this. We present results that reveal for the first time a qualitative thermodynamic difference between the high temperature and deeply supercooled equilibrium glass-forming liquid: the influence of boundary conditions propagates into the bulk over larger and larger lengthscales upon cooling, and, as this static correlation length grows, the influence decays nonexponentially. Increasingly long-range susceptibility to boundary conditions is expected within the random firt-order theory (RFOT) of the glass transition, but a quantitative account of our numerical results requires a generalization of RFOT where the surface tension between states fluctuates.