A direct measurement of the quasiparticle trapping efficiency for a normal metal trap

We present preliminary measurements intended to directly probe the efficiency at which energy is transferred from quasiparticles in a large-area superconductor film to conduction electrons in a smaller, normal metal trap. Quasiparticle excitations are injected into a superconductor film by a normal-insulator-superconductor (NIS) tunnel junction. These excitations diffuse throughout the superconductor and are eventually trapped by an adjoining normal metal film. The power deposited in electrons in the trap is measured by a second NIS junction, where part of the metal trap forms the normal electrode. The efficiency of the trap is the ratio of absorbed to incident power. For an Al superconductor film and a Ag trap we measure a trapping efficiency of at least 10% near 100 mK.