Spectral Shape of Relaxations in Silica Glass

Precise low-frequency light scattering experiments on silica glass are presented, covering a broad temperature and frequency range ( $9\mathrm{GHz}<\nu <2\mathrm{THz}$). The spectra show a power-law low-frequency wing of the relaxational part of the spectrum with an exponent $\alpha$ proportional to temperature in the range $30<T<\mathrm{}200\mathrm{K}$. A comparison of our results with those from acoustic attenuation experiments performed at different frequencies shows that this power-law behavior rather well describes relaxations in silica over 9 orders of magnitude in frequency. These findings can be explained by a model of thermally activated transitions in double well potentials.