The Effects of Hot Phonon Irradiation on the Superconducting Transition of Thin Aluminium Films

Substantial deviations from the equilibrium superconducting state can be easily generated in thin film samples. The pair breaking effect of incident photons has been observed in such films [1], and in the present work we have looked for its analogue for the case of phonon irradiation. We have so far been concerned only with Al films on sapphire substrates. The sapphire crystals were cylindrical, and the Al films were typically 100–200 nm thick. Phonon pulses were generated electrically in a constantan heater ∿ 20 nm thick.