Acoustic damping in Li$_2$O-2B$_2$O$_3$ glass observed by inelastic x-ray and optical Brillouin scattering

TL;DR

This study investigates acoustic damping in lithium diborate glass using inelastic x-ray and Brillouin scattering, revealing a high-power Q-dependence below the crossover and linking damping to resonance with boson peak modes.

Contribution

It provides new insights into the damping behavior of acoustic waves in glasses and demonstrates the hybridization with boson peak modes as the cause of acoustic branch termination.

Findings

Linewidth increases with a high power of Q below crossover

Damping linked to resonance with boson peak modes

Simple quadratic dependence of damping is ruled out

Abstract

The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer $Q$ using high resolution inelastic x-ray scattering. Much attention has been devoted to the low $Q$-range, below the observed Ioffe-Regel crossover \qco{}$\simeq$ 2.1 nm$^{-1}$. We find that below \qco{}, the linewidth of longitudinal acoustic waves increases with a high power of either $Q$, or of the frequency $\Omega$, up to the crossover frequency \OMco{} $\simeq$ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple $\Omega^2$-dependence of the acoustic damping over the entire frequency range.