A simple and broadly-applicable definition of shear transformation zones

TL;DR

This paper introduces a simple, harmonic-approximation-based definition of shear transformation zones (STZs) in amorphous solids, providing a broadly applicable method to identify plasticity precursors in glasses and colloids.

Contribution

It proposes a new, harmonic approximation-based definition of STZs that is more broadly applicable than previous anharmonic methods.

Findings

The new definition effectively identifies STZs in computer simulations.

The method is applicable to laboratory materials like dense colloidal suspensions.

An open-source library for analyzing STZs is provided.

Abstract

Plastic deformation in amorphous solids is known to be carried by stress-induced localized rearrangements of a few tens of particles, accompanied by the conversion of elastic energy to heat. Despite their central role in determining how glasses yield and break, the search for a simple and generally applicable definition of the precursors of those plastic rearrangements -- the so-called shear transformation zones (STZs) -- is still ongoing. Here we present a simple definition of STZs -- based solely on the harmonic approximation of a glass' energy. We explain why and demonstrate directly that our proposed definition of plasticity carriers in amorphous solids is more broadly applicable compared to anharmonic definitions put forward previously. Finally, we offer an open-source library that analyzes low-lying STZs in computer glasses and in laboratory materials such as dense colloidal suspensions for which the harmonic approximation is accessible. Our results constitute a physically motivated methodological advancement towards characterizing mechanical disorder in glasses, and understanding how they yield.