Amorphous Order & Non-linear Susceptibilities in Glassy Materials

TL;DR

This paper reviews 15 years of research on the non-linear response of glassy materials, highlighting how growing amorphous order influences susceptibilities and supports the RFOT theory over kinetic models.

Contribution

It synthesizes theoretical and experimental evidence linking non-linear susceptibilities to amorphous order, emphasizing RFOT predictions and challenging kinetic theories.

Findings

Non-linear susceptibilities grow with temperature decrease or aging.

Experimental data align with RFOT predictions of increasing 'glassites'.

Kinetic theories struggle to explain the observed behaviors.

Abstract

We review 15 years of theoretical and experimental work on the non-linear response of glassy systems. We argue that an anomalous growth of the peak value of non-linear susceptibilities is a signature of growing "amorphous order" in the system, with spin-glasses as a case in point. Experimental results on supercooled liquids are fully compatible with the RFOT prediction of compact "glassites" of increasing volume as temperature is decreased, or as the system ages. We clarify why such a behaviour is hard to explain within purely kinetic theories of glass formation, despite recent claims to the contrary.