Phase memory effects in mesoscopic rings with superconducting ‘‘mirrors’’

Abstract

We find a drastic difference between the magnetoresistance of normal-metal (Ag) mesoscopic rings with superconducting boundaries (mirrors) and that of plain rings. The amplitude of h/2e Aharanov-Bohm oscillations is enhanced more than 100 times in rings with mirrors in the measuring leads. Rings with mirrors in stubs perpendicular to the current flow show h/4e and h/2e oscillations and evidence of a superconducting transition. The resutls are interpreted as due to a phase coupling between the superconductors via normal electrons, and to a confinement of quasiparticles to the ring by Andreev reflections.