Quasiparticle Propagation and Recombination in Bulk, Superconducting Pb

The propagation characteristics of quasiparticles in bulk superconducting Pb single crystals is studied. A transition from quasiparticle diffusion to diffusion of the combined gas of quasiparticles and phonons is observed as the temperature is increased. The intrinsic quasiparticle recombination time, as well as the decay time of the quasiparticle density, is determined. The latter is found to be at least an order of magnitude longer than this quasiparticle recombination time.