Short-Time-Scale Measurement of the Low-Temperature Specific Heat of Polymethyl Methacrylate and Fused Silica

Low-temperature specific-heat measurements of amorphous silica and polymethyl methacrylate have been performed on a 10^-4-sec time scale using a novel heat-pulse technique. The data disagree with a recent theoretical prediction of Phillips and of Anderson et al. This prediction is based on the assumption that tunneling states are the origin of both the linear temperature dependence of the specific heat and the T² temperature dependence of the thermal conductivity characteristic of all glasses at low temperatures.