Low-energy quasilocalized excitations in structural glasses

TL;DR

This paper reviews three decades of research on low-energy quasilocalized excitations in structural glasses, highlighting their universal properties and significance for understanding glassy thermomechanical behaviors.

Contribution

It provides a comprehensive overview of the emergence, statistical, and structural properties of QLEs in glasses, emphasizing recent advances and future challenges.

Findings

QLEs are universal features in glasses affecting their thermomechanical properties

Recent simulations reveal self-organization leads to QLE emergence during vitrification

Understanding QLEs is key to explaining glassy anomalies and failure mechanisms

Abstract

Glassy solids exhibit a wide variety of generic thermomechanical properties, ranging from universal anomalous specific heat at cryogenic temperatures to nonlinear plastic yielding and failure under external driving forces, which qualitatively differ from their crystalline counterparts. For a long time, it has been believed that many of these properties are intimately related to nonphononic, low-energy quasilocalized excitations (QLEs) in glasses. Indeed, recent computer simulations have conclusively revealed that the self-organization of glasses during vitrification upon cooling from a melt leads to the emergence of such QLEs. In this Perspective Article, we review developments over the past three decades towards understanding the emergence of QLEs in structural glasses, and the degree of universality in their statistical and structural properties. We discuss the challenges and difficulties that hindered progress in achieving these goals, and review the frameworks put forward to overcome them. We conclude with an outlook on future research directions and open questions.