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Time-Dependent Specific Heat in Vitreous Silica Using Diffusivity Measurement

Pulsed diffusivity measurement of vitreous silica with the sample immersed in liquid helium has been performed. The observed short-time diffusivity is in good agreement with the dc diffusivity over the temperature range from 1.5 K to 3.9 K, which is consistent with the earlier diffusivity measurements. Our result at 1.5 K is, however, not consistent with the time-dependent specific heat measurement in an adiabatic sample arrangement. This may be due to the different sample-to-bath time constants. The diffusivity at low temperatures seems to remain an unsolved problem.