Disentangling hierarchical relaxations in glass formers via dynamic eigenmodes

TL;DR

This paper introduces a dynamic eigenmode approach to dissect the hierarchical relaxation processes in glass-forming systems, revealing five distinct mode classes that elucidate the microscopic organization of dynamics across timescales.

Contribution

It presents a novel microscopic framework combining particle observations with eigenmode analysis to classify and understand relaxation modes in glass formers.

Findings

Identification of five classes of relaxation modes.

Quasi-elastic modes mark the onset of glassy dynamics.

Reversible string modes dominate dynamic heterogeneity.

Abstract

Hierarchical dynamics in glass-forming systems span multiple timescales, from fast vibrations to slow structural rearrangements, appearing in both supercooled fluids and glassy states. Understanding how these diverse processes interact across timescales remains a central challenge. Here, by combining direct particle-level observations with a dynamic eigenmode approach that decomposes intermediate-timescale responses into distinct modes, we reveal the microscopic organisation of relaxation dynamics in two-dimensional colloidal systems. We identify five classes of modes characterizing hierarchical dynamics: (i) quasi-elastic modes, (ii) slow-reversible string modes contributing to dynamic heterogeneity, (iii) slow-irreversible string modes leading to flow, (iv) fast-$\beta$ modes with fast-reversible strings, and (v) random noise modes. The emergence of quasi-elastic modes marks the onset of glassy dynamics, while reversible string modes dominate dynamic heterogeneity throughout both supercooled and glassy regimes. Our findings offer a unified microscopic framework for understanding how distinct relaxation processes interconnect across timescales, illuminating the mechanisms driving glass formation.