ac effect in the conductance of mesoscopic normal-metal–superconductor structures

Resonant peaks in the resistance of a mesoscopic normal-metal wire in contact with two superconductors under rf irradiation are detected. The peaks occur when a potential difference VS=ω/2e is applied between the superconductors. The peaks can be interpreted as an ac phase-coherent phenomenon in the conductance of mesoscopic normal-metal--superconductor structures. This effect is observed although the critical Josephson current is negligibly small and the Shapiro steps are absent.