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-dimensional electron gas as the phase-coherent normal conductor. In low magnetic fields, h/2e periodic conductance oscillations due to phase-conjugated Andreev reflections are observed with an amplitude delta G similar or equal to 0.10e(2)/h at T = 50 mK. These oscillations are suppressed by a flux of approximately h/e through the interference region, For larger magnetic fields, sample-specific h/2e conductance oscillations are found with delta G = 0.005e(2)/h. No indication is found for an intrinsic h/4e periodic superconductor-modified weak localization contribution.