Quartic Scaling of Sound Attenuation with Frequency in Vitreous Silica

Abstract

Many theories predict a quartic increase of the acoustic damping at sub-THz frequencies in glassy media, related to the excess vibrational modes known as the boson peak anomaly. Here by introducing phase-sensitive acoustic spectroscopy techniques with a THz bandwidth, we investigate the acoustic properties of vitreous silica at 15 and 300 K in the crucial but unexplored sub-THz gap region below the boson peak. Our results indicate a negative dispersion below the THz range and the onset of an athermal quartic frequency scaling acoustic attenuation term, which appears above all other thermal losses.