Bond-space operator disentangles quasi-localized and phononic modes in structural glasses

TL;DR

This paper introduces a bond-space operator that effectively isolates quasi-localized modes in structural glasses, overcoming previous spectral analysis limitations caused by phononic hybridization and system size effects.

Contribution

The study develops a novel bond-force-response operator that disentangles QLMs from phononic modes, providing clearer insights into their properties and dependence on material preparation.

Findings

The operator isolates QLMs from phononic modes in vibrational spectra.

QLMs' density and spatial extent depend on annealing protocols.

The method offers a new interpretation of QLMs in disordered materials.

Abstract

The origin of several emergent mechanical and dynamical properties of structural glasses is often attributed to populations of localized structural instabilities, coined quasilocalized modes (QLMs). Under a restricted set of circumstances, glassy QLMs can be revealed by analyzing computer glasses' vibrational spectra in the harmonic approximation. However, this analysis has limitations due to system-size effects and hybridization processes with low energy phononic excitations (plane waves) that are omnipresent in elastic solids. Here we overcome these limitations by exploring the spectrum of a linear operator defined on the space of particle interactions (bonds) in a disordered material. We find that this bond-force-response operator offers a unique interpretation of QLMs in glasses, and cleanly recovers some of their important statistical and structural features. The analysis presented here reveals the dependence of the number density (per frequency) and spatial extent of QLMs on material preparation protocol (annealing). Finally, we discuss future research directions and possible extensions of this work.