Anharmonic properties of vibrational excitations in amorphous solids

TL;DR

This paper investigates the anharmonic vibrational properties in amorphous solids, revealing strong localized anharmonicities that induce particle rearrangements, which are essential for understanding their thermal behavior.

Contribution

It provides the first detailed analysis of anharmonicities in both phonon-like and quasi-localized modes in amorphous solids, highlighting their role in particle rearrangements.

Findings

Vibrational modes exhibit strong anharmonicities.

Anharmonicities induce localized particle rearrangements.

Rearrangements involve 1 to 1000 particles.

Abstract

Understanding the vibrational and thermal properties of amorphous solids is one of the most discussed and long-standing issues in condensed matter physics. Recent works have made significant steps towards understanding harmonic vibrational states. In particular, it has been established that quasi-localized vibrational modes emerge in addition to phonon-like vibrational modes. In this work, we study the anharmonic properties of these vibrational modes. We find that vibrational modes exhibit anharmonicities that induce particle rearrangements and cause transitions to different states. These anharmonicities are distinct from those in crystals, where particle rearrangements never occur. Remarkably, for both the phonon modes and quasi-localized modes, the vibrational modes exhibit strong anharmonicities, and the induced particle rearrangements are always localized in space and are composed of 1 to 1000 particles. Our findings contribute to the understanding of low-temperature thermal properties, for which anharmonic vibrations are crucial.