Observation of Time-Dependent Specific Heat in Amorphous Si${\mathrm{O}}_2$

The time-dependent specific heat of amorphous Si${\mathrm{O}}_2$ has been measured between 0.1 and 1 K over the range ∼ 1 sec to 10 μsec. The decoupling of the roughly $T$-dependent contribution to specific heat is observed in submillisecond time scales, in qualitative agreement with the predictions of the tunneling model. However, the excess $T^3$-dependent specific heat is not decoupled on the time scales involved.