Intermittent rearrangements accompanying thermal fluctuations distinguish glasses from crystals

TL;DR

This paper reveals that glasses exhibit unique intermittent particle rearrangements during thermal fluctuations, driven by anharmonic processes, which differentiate their behavior from crystals and are crucial for understanding glass dynamics.

Contribution

It uncovers a new anharmonic channel causing intermittent rearrangements in glasses, expanding understanding beyond harmonic approximations and phonon-phonon interactions.

Findings

Thermal vibrations induce transitions within the same energy basin.

Rearrangements are distinct from diffusion and aging.

These processes are key to distinguishing glasses from crystals.

Abstract

It is a persistent problem in condensed matter physics that glasses exhibit vibrational and thermal properties that are markedly different from those of crystals. While recent works have advanced our understanding of vibrational excitations in glasses at the harmonic approximation limit, efforts in understanding finite-temperature anharmonic processes have been limited. It is well known that phonons in crystals couple through phonon-phonon interactions, an extremely efficient mechanism for anharmonic decay that is also important in glasses. Here, however, we show that an additional anharmonic channel of different origin emerges in the case of glasses, which induces intermittent rearrangements of particles. We have found that thermal vibrations in glasses trigger transitions among numerous different local minima of the energy landscape, which, however, are located within the same wide (meta)basin. These processes generate motions that are different from both diffusive and out-of-equilibrium aging dynamics. We suggest that the intermittent rearrangements accompanying thermal fluctuations are crucial features distinguishing glasses from crystals.