Additional Evidence for TLS in Electron-Irradiated Quartz from Ultrasonic Attenuation Measurements

Abstract

At low temperatures amorphous solids exhibit dynamical properties which are unexpectedly different from these in crystals.[1] They can be attributed to the existence of configurational tunneling states,[2] which are successfully described as two-level systems(TLS).[3] The microscopic origin of these TLS is not clear yet. In an attempt to contribute to this study, crystalline solids with defects, like irradiated crystals, have been investigated. Similar anomalies as in glasses were observed in slightly neutron-irradiated quartz.[4,5,6,7] They were explained by the presence of TLS with a density of states which is smaller than in vitreous silica and which increases with neutron dose. In an earlier stage of our research one of us was involved in low-temperature thermal conductivity studies [8,9] in electron irradiated quartz. These measurements gave evidence for the presence of TLS. However it was not generally accepted that electrons could induce TLS. Here we present conclusive evidence for the existence of TLS in electron-irradiated quartz from ultrasonic studies carried out in a temperature range 1.4 to 300 K. A more detailed discussion can be found in ref.[10].