SAMPLE-SPECIFIC CONDUCTANCE FLUCTUATIONS MODULATED BY THE SUPERCONDUCTING PHASE

We have studied sample-specific conductance fluctuations tuned by the phase difference between superconducting boundaries, using a two-dimen sional electron gas as the phase-coherent normal conductor. In low mag netic fields, h/2e periodic conductance oscillations due to phase-conj ugated Andreev reflections are observed with an amplitude delta G simi lar or equal to 0.10e(2)/h at T = 50 mK. These oscillations are suppre ssed by a flux of approximately h/e through the interference region, F or larger magnetic fields, sample-specific h/2e conductance oscillatio ns are found with delta G = 0.005e(2)/h. No indication is found for an intrinsic h/4e periodic superconductor-modified weak localization con tribution.