Experimental Evidence on Time-Dependent Specific Heat in Vitreous Silica

Measurements have been made of the heat capacity of thin plates of vitreous silica between 0.35 and 1.6 K. In an adiabatic sample arrangement the time-resolved specific heat was measured over a time scale from 2 {μ}sec to 0.5 msec. The observed time dependence of the heat capacity is in quite good agreement with the tunneling model, which predicts a logarithmic increase in time. In addition, a much stronger time dependence was observed above 1 K, which was interpreted as a decoupling of excess modes from the Debye phonons.