Mesoscopic Transport in Tunable Andreev Interferometers

Abstract

Low temperature transport measurements have been performed on nanofabricated Au wires a few \ensuremath{\mu}m long contacting two Nb electrodes whose superconducting phase difference $\ensuremath{\Delta}\ensuremath{\theta}$ was externally controlled. $\ensuremath{\Delta}\ensuremath{\theta}$ was generated by passing a known supercurrent through a series array of $28 \mathrm{N}\mathrm{b}\ensuremath{-}\mathrm{A}\mathrm{l}{\mathrm{O}}_{x}\ensuremath{-}\mathrm{N}\mathrm{b}$ Josephson junctions. The conductance of the Au wire displays a component in $\ensuremath{\Delta}\ensuremath{\theta}$ with period $2\ensuremath{\pi}$. These conductance oscillations arise from the change in scattering boundary conditions of quasiparticles in the Au wire at the Au-Nb interfaces due to Andreev reflection.