Proximity-induced josephson-quasiparticle process in a single-electron transistor

We have performed experiments in a superconductor–normal-metal–superconductor single-electron transistor in which there is an extra superconducting strip partially overlapping the normal-metal island in good metal-to-metal contact. The superconducting proximity effect gives rise to current peaks at voltages below the quasiparticle threshold. We interpret these peaks in terms of the Josephson-quasiparticle process and discuss their connection with the proximity-induced energy gap in the normal-metal island.