GIANT CONDUCTANCE OSCILLATIONS IN MESOSCOPIC ANDREEV INTERFEROMETERS

We analyse the electrical conductance G(phi) of a two-dimensional, pha se-coherent structure in contact with two superconductors, which is kn own to be an oscillatory function of the phase difference phi between the superconductors. It is predicted that for a ballistic sample, the amplitude of oscillation will be enhanced by placing a normal barrier at the normal-superconducting interface, and that by tuning the streng th of the barrier, it can be made orders of magnitude greater than val ues observed in recent experiments. Giant oscillations can also be obt ained without a barrier, provided that a crucial sum rule is broken. T his can be achieved by disorder-induced normal scattering. In the abse nce of zero-phase inter-channel scattering, the conductance possesses a zero-phase minimum and a maximum at phi = pi.