The origin of sound damping in glasses: Defects and beyond

Comprehending sound damping is integral to understanding the anomalous low temperature properties of glasses. After decades of studies, Rayleigh scaling of the sound attenuation coefficient with frequency, Γ∽ω^(d+1), became generally accepted. Rayleigh scaling invokes a picture of scattering from defects. It is, however, unclear how to define glass defects. We use a particle level contribution to sound damping to determine areas in the glass that contribute more to sound damping than other areas, which allows us to define defects. Over a range of stability, sound damping scales linearly with the fraction of particles in the defects. However, sound is still attenuated in ultrastable glasses where no defects are identified. We show that sound damping in these glasses is due to nearly uniformly distributed non-­affine forces that arise after macroscopic deformation. To fully understand sound attenuation in glasses, one has to consider contributions from defects and a defect-­free background, which represents a different paradigm of sound damping in glasses.