Low-temperature specific heat of rare-earth-doped silicate glasses

Abstract

The specific heat (Formula presented) of (Formula presented)- and (Formula presented)-doped silicate glasses has been determined between 0.1 and 10 K. Below about 5 K, (Formula presented)∝(Formula presented) with ν=0.0-0.3. This dependence is characteristic for the two-level-system (TLS) contribution to the specific heat, (Formula presented). The values of (Formula presented) and ν noticeably vary with the chemical nature and the concentration of the glass modifiers. The number of TLS in samples of almost identical composition is significantly larger for the (Formula presented) doped than for the (Formula presented) doped and the undoped glass. Above 5 K, the (Formula presented)-phonon term and the (Formula presented) term associated with soft localized vibrations also contribute to (Formula presented). The results do not point to a correlation between the (Formula presented) and the higher-order terms. © 1996 The American Physical Society.