We report the experimental observation of the recently predicted peaks on the $I-V$ curve of a superconducting single-electron transistor at relatively high temperatures. The peaks are due to the matching of singularities in the quasiparticle density of states in two electrodes of a tunnel junction. The energy shift due to Coulomb blockade provides the matching at finite voltage.

• Received 18 April 1997

DOI:https://doi.org/10.1103/PhysRevB.56.5116