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 large h/2e-periodic oscillations with 1/T power law decay. This flux-sensitive contribution arises from coherence of low-energy quasiparticles states over the phase-breaking length L_ϕ. Mesoscopic fluctuations contribute as a small h/e oscillation, resolved only in the purely normal state.

4 pages, 3 figures