Andreev-reflection-induced conductance diffraction in mesoscopic normal-metal/superconductor interfaces

We observed conductance oscillations, which arose from the interference of quasiparticles Andreev-reflected from a mesoscopic, single normal-metal/superconductor (N/S) interface with a phase gradient along its width. A 10 × 10 μm² Al island was overlaid on a pre-evaporated 0.5-μm-wide silver wire. The phase gradient along the N/S interface was induced by applying a magnetic field perpendicular to the plane of the superconducting Al island. The conductance across the N/S interface showed Fraunhofer-like oscillations with amplitudes of a small fraction of 2e²/h. For sufficiently low fields and temperatures, this interfacial diffraction effect of quasiparticles is more complicated due to the field-induced electron-hole dephasing effect. The overall magnetic-field and temperature dependencies of the conductance oscillations are qualitatively consistent with the predicted diffraction of Andreev-reflected quasiparticles.