Sound attenuation in glasses

Comprehending sound attenuation is integral to understanding the anomalous low temperature properties of glasses. Despite decades of studies, the underlying mechanism of sound attenuation in glasses is still debated. In this perspective, we review recent work on sound attenuation in amorphous solids. We focus on the role of defects and heterogeneous elasticity, and we also discuss attenuation in model amorphous solids without defects. We review our definition of attenuation defects and show that they strongly influence sound attenuation. However, we also find another contribution to sound attenuation that cannot be attributed to attenuation defects. We confirm an earlier result of Kapteijns et al. [Kapteijns et al., J. Chem. Phys. 154, 081101 (2021)] that heterogeneous elasticity theory predicts relative changes of sound attenuation in model two-dimensional glasses if the configuration-to-configuration elastic constants fluctuations are used to quantify the heterogeneity. We extend this finding to similar three-dimensional glasses. We end by discussing the Euclidean random matrix model, which exhibits Rayleigh scaling of sound attenuation but does not have quasi-localized excitations and, thus, probably does not have sound attenuation defects. We propose that the mechanisms behind sound attenuation can be more fully understood by approaching the problem from two directions: one where the strong influence of defects is studied and another where sound attenuation is studied in defect free, although disordered, materials.