Quasiparticle transport properties of mesoscopic wires containing normal-metal/superconductor/normal-metal proximity junctions

We measured the differential resistance dV/dI of mesoscopic normal-metal/superconductor/ normal-metal (N-S-N) junctions. At low temperatures (T < 4 K), we observed a dip in dV/dI at zero bias and anomalous peaks near a bias of 2 Delta(PbIn)/e, where Delta(PbIn) is the gap energy of superconducting Pb-In, and at a higher bias V-c. The zero-bias dip is supposed to originate from Andreev reflections of quasiparticles and the peak near 2 Delta(PbIn)/e from the formation of a standing-wave mode of quasiparticles inside the superconducting potential barrier. We attribute the peaks at V-c to a transition of the superconducting region to the normal state as the current exceeds the critical current I-c of S.