Acoustic mismatch model and thermal phonon radiation across a tin/sapphire interface with radiation temperatures between 1.6 and 3.7 K

Abstract

Using a special sandwich arrangement consisting of a constantan film, an insulating oxide layer and a superconducting tin-tunnel junction evaporated on an a-cut sapphire, the temperature jump between tin and sapphire has been measured as function of thermal phonon flux under steady-state and transient conditions using rectangular current pulses in the constantan heater. The tunnel junction serves as a very fast thermometer with a time resolution in the nanosecond range. During the steady-state and the heatup interval, full agreement is found between experimental results, and the predictions of the acoustic mismatch model applied to the phonon transfer across the tin/sapphire interface and under the additional assumption that thermal equilibrium exists between electrons and phonons (‘one-temperature model’). In contrast, very strong deviations are found during the cooling process which starts immediately after the end of the heating pulses. This observed nonequilibrium between electron and phonon system is discussed in more detail in a subsequent paper.