Very-low-frequency Raman scattering in vitreous silica

Abstract

The very-low-frequency Raman scattering from vitreous silica was measured for frequency shifts $\omega$ as small as 4 ${\mathrm{cm}}^{-1\mathrm{}}$. The data were compared with present theories on disorder-induced sacttering; for $\omega <20\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ an excess scattered intensity was found, which is not seen in the corresponding crystalline state. The magnitude of this excess intensity was determined relative to that of the Brillouin lines; its temperature dependence was found to be stronger than one-phonon processes, but weaker than two-phonon processes. We discuss the excess scattering in terms of existing models for the low-temperature specific heat of glasses and find, at least for temperatures $T>\mathrm{}80\mathrm{}$ K, our data to be consistent with disorder-induced scattering from damped high-frequency sound waves.