Observation of conductance oscillations in a superconducting Andreev diffractometer

Abstract

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 x 10 mum(2) Al patch was overlaid on a pre-evaporated 0.5-mum-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 2e(2)/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. (C) 2001 Elsevier Science B,V. All rights reserved.