Low temperature thermal properties and intrinsic defects in vitreous silica

Measurements of the low temperature specific heatC _p (0.04KT2.4K) and thermal conductivityk (0.5KT20K) of high purity vitreous silica (Suprasil W) in the as-received and electron-irradiated states are reported. In the temperature range where the localized excitations inherent in glasses dominateC _p (T0.5K) no change is observed upon electron irradiation of up to 10¹⁹e^– (total dose). An anomalyC around 1.8K is observed inC _p which is reduced by 40% upon irradiation. However, ask is not affected by electron irradiation, localized excitations as origin forC can be ruled out. The density of paramagnetic centers in the most heavily irradiated sample is 510¹⁷cm^–3 as obtained from the ESR signal. It has been suggested that these centers have diamagnetic precursors in the unirradiated glass. Our measurements indicate that those defects are not associated with the localized excitations.