Phase-coherent conduction in mesoscopic normal-metal/superconductor hybrid junctions

In this paper we report about the transport properties of mesoscopic normal-metal/superconductor (NS) hybrid systems with two different junction layouts. One is a junction fabricated by overlaying S on N wire and the other with S sandwiched between two N wires, forming an NSN structure. At zero bias all the junctions exhibited a sharp decrease of dV/dI, which is believed to arise from the interference between the disorder-scattered and the Andreev-reflected quasiparticles. A small magnetic field corresponding to one flux quantum through the normal metal region, applied in parallel with the NS junction, easily suppressed the anomalous zero-bias conductance enhancement for the sandwich-junction sample. This high sensitivity to a small magnetic field observed in our systems of mesoscopic NS junctions in a diffusive-transport regime directly confirms the electron-hole-interference origin of the zero-bias anomaly.