Most recent experiments on nonequilibrium superconductors have been interpreted in terms of a theoretical model that assumes the recombination time of quasiparticles acts as a bottleneck in the quasiparticle relaxation process. However, in all experiments to date, the actual bottleneck is the escape time of recombination phonons from the superconductor. We show that all previous experiments can be interpreted in terms of a modified heating theory where the quasiparticles remain in both thermal and chemical equilibrium at an effective temperature $T^{*}$ greater than the helium-bath temperature. The temperature $T^{*}$ is determined from a consideration of only those phonons with energy greater than $2\Delta$.

• Received 2 April 1975

DOI:https://doi.org/10.1103/PhysRevB.12.3667