A note on slow- and fast-relaxing low-energy excitations in vitreous silica

Abstract

The coexistence of slow- and fast-relaxing low-energy excitations in vitreous silica is analysed, on account of experimental data concerning the very low-temperature (T<0.1 K) specific heat, on the one hand, and the thermal response of low-energy excitations, on the other hand. It is shown that the application of the tunnelling atom theory to both the above-mentioned experimental results leads to contradictory conclusions, if a single set of two-level systems is assumed. An experiment is suggested in order to test the possibility of a double set of two-level systems ina-SiO2.