High-frequency propagating modes in vitreous silica at 295 K

Abstract

Collective modes in vitreous silica (v-${\mathrm{SiO}}_{2}$) are found at 295 K and at momentum transfers Q=1.5 and 2.0 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$. They propagate with a sound velocity of \ensuremath{\approx} 6000 m/s, a value equivalent to that in the Q\ensuremath{\rightarrow}0 limit, and to that recently measured at 1050 K in the 1--3.5 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$ Q range. The data complete the scenario on the acousticlike dynamics in v-${\mathrm{SiO}}_{2}$, showing its temperature independence and propagating rather than localized nature in the whole 295--1050 K and 0.01--2.0 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$ temperature and Q ranges.