Observation of conductance oscillations in a superconducting Andreev diffractometer

We observed superconductivity-induced conductance oscillations, arising from quasiparticle interference effects in a single normal-metallic (N) electrode of finite width in contact with a superconductor (S). A 10 × 10 μm² Al patch was overlaid on a pre-evaporated 0.5-μm-wide mesoscopic silver wire. A phase gradient along the N/S interface was induced by applying a magnetic field perpendicular to the plane of the superconducting Al patch. The conductance across the N/S interface showed Fraunhofer-like oscillations with amplitudes of a small fraction of 2e²/h per conducting channel, for fields up to 450 G. For sufficiently low fields and temperatures the interfacial diffraction effect of quasiparticles is more complicated due to the field-induced electron-hole dephasing effect. None the less, the overall feature of the oscillatory magnetoconductance from the N/S interface appears to confirm the diffraction of Andreev-reflected quasiparticles proposed theoretically for a single N/S interface with a phase gradient.