Long-Range Coherence in a Mesoscopic Metal near a Superconducting Interface

Abstract

We identify the different contributions to quantum interference in a mesoscopic metallic loop in contact with two superconducting electrodes. At low temperature, a flux-modulated Josephson coupling is observed with strong damping over the thermal length ${L}_{T}$. At higher temperature, the magnetoresistance exhibits $h/2e$-periodic oscillations with $1/T$ power law decay. This flux-sensitive contribution arises from coherence of low-energy quasiparticle states over the phase-breaking length ${L}_{\ensuremath{\phi}}$. Mesoscopic fluctuations contribute as a small $h/e$ oscillation, resolved only in the purely normal state.