High frequency dynamics in a monatomic glass

TL;DR

This study investigates high frequency dynamics in glassy Selenium using Inelastic X-ray Scattering, revealing dispersing acoustic modes and a quadratic relation between sound attenuation and frequency, clarifying previous experimental and numerical discrepancies.

Contribution

It provides detailed high-quality data confirming the existence of dispersing acoustic modes and establishes a generalized quadratic law for sound attenuation in glassy Selenium.

Findings

Dispersing acoustic mode observed for 1.5<Q<12.5 nm$^{-1}$

Sound velocity exceeds hydrodynamic value by ~10% at low Q

Sound attenuation follows a $ ext{Gamma}(Q) ext{propto} ext{Omega}(Q)^2$ law

Abstract

The high frequency dynamics of glassy Selenium has been studied by Inelastic X-ray Scattering at beamline BL35XU (SPring-8). The high quality of the data allows one to pinpoint the existence of a dispersing acoustic mode for wavevectors ($Q$) of $1.5<Q<12.5$ nm$^{-1}$, helping to clarify a previous contradiction between experimental and numerical results. The sound velocity shows a positive dispersion, exceeding the hydrodynamic value by $\approx$ 10% at $Q<3.5$ nm$^{-1}$. The $Q^2$ dependence of the sound attenuation $\Gamma(Q)$, reported for other glasses, is found to be the low-$Q$ limit of a more general $\Gamma(Q) \propto \Omega(Q)^2$ law which applies also to the higher $Q$ region, where $\Omega(Q)\propto Q$ no longer holds.