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.
تحميل البحث