Theory of harmonic dissipation in disordered solids

TL;DR

This paper develops an analytical model for harmonic energy dissipation in disordered solids, validated by simulations on amorphous silica, revealing that oxygen atom motions primarily contribute to dissipation.

Contribution

It introduces an analytical expression for high-frequency dissipation in glasses and links dissipation to atomic-scale structural dynamics, validated by molecular dynamics simulations.

Findings

Analytical formula for harmonic dissipation in glasses.

Dissipation arises from non-affine relaxations and vibrational modes.

Oxygen atom motions mainly drive energy loss in silica.

Abstract

Mechanical spectroscopy, i.e. cyclic deformations at varying frequencies, is used theoretically and numerically to measure dissipation in model glasses. From a normal mode analysis, we show that in the high-frequency THz regime where dissipation is harmonic, the quality factor (or loss angle) can be expressed analytically. This expression is validated through non-equilibrium molecular dynamics simulations applied to a model of amorphous silica (SiO$_2$). Dissipation is shown to arise from non-affine relaxations triggered by the applied strain through the excitation of vibrational eigenmodes that act as damped harmonic oscillators. We discuss an asymmetry vector field, which encodes the information about the structural origin of dissipation measured by mechanical spectroscopy. In the particular case of silica, we find that the motion of oxygen atoms, which induce a deformation of Si-O-Si bonds is the main contributor to harmonic energy dissipation.