Irreversible reorganization in a supercooled liquid originates from localised soft modes

TL;DR

This paper demonstrates that localized soft modes in supercooled liquids are causally linked to irreversible structural reorganization, enabling a new theory of relaxation without relying on dynamics.

Contribution

It reveals the causal relationship between soft local modes and structural reorganization, providing a basis for a static theory of relaxation in glass-forming liquids.

Findings

Localized low frequency modes correlate with irreversible reorganization

Spatial distribution of soft modes persists despite particle rearrangements

Potential to develop a static relaxation theory in glasses

Abstract

The transition of a fluid to a rigid glass upon cooling is a common route of transformation from liquid to solid that embodies the most poorly understood features of both phases1,2,3. From the liquid perspective, the puzzle is to understand stress relaxation in the disordered state. From the perspective of solids, the challenge is to extend our description of structure and its mechanical consequences to materials without long range order. Using computer simulations, we show that the localized low frequency normal modes of a configuration in a supercooled liquid are causally correlated to the irreversible structural reorganization of the particles within that configuration. We also demonstrate that the spatial distribution of these soft local modes can persist in spite of significant particle reorganization. The consequence of these two results is that it is now feasible to construct a theory of relaxation length scales in glass-forming liquids without recourse to dynamics and to explicitly relate molecular properties to their collective relaxation.