Quasiparticle trapping from a single-crystal superconductor into a normal-metal film via the proximity effect

We have studied the dynamics of the nonequilibrium state produced in single-crystal superconducting indium by pulsed laser irradiation using tunnel junctions. By a suitable choice of a thin metal film in intimate contact with the indium crystal, we have been able to produce a pronounced change in the time evolution of the excess quasiparticle density which indicates that the quasiparticles are trapped in the film. This effect can take place both when the film is another superconductor of lower energy gap or is a normal metal made superconducting by the proximity effect.