Quartic scaling of sound attenuation with frequency in vitreous silica

TL;DR

This study uses advanced THz acoustic spectroscopy to reveal a quartic frequency dependence of sound attenuation in vitreous silica at sub-THz frequencies, confirming theoretical predictions about vibrational modes.

Contribution

It introduces phase-sensitive THz acoustic spectroscopy to measure attenuation in vitreous silica, uncovering a quartic frequency-scaling behavior in a previously unexplored spectral region.

Findings

Strong negative dispersion begins at 500 GHz

Quartic frequency-scaling attenuation emerges above thermal losses

Attenuation behavior aligns with boson peak anomaly theories

Abstract

Many theories predict a quartic acoustic attenuation increase at sub-THz frequencies in glassy media for 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 300K in the crucial but unexplored sub-THz gap region below the boson peak. Our results indicate a strong negative dispersion starting at \SI{500}{GHz} and the onset of an athermal quartic-frequency-scaling acoustic attenuation term, which emerges above all other thermal losses.