INFLUENCE OF ELECTRONIC INTERFERENCES ON THE ANDREEV CONDUCTANCE

We have performed an interference experiment with two tunnel junctions between a thin normal metal wire and a superconducting fork. We have found that the subgap current is strongly modulated by the difference between the superconducting phases at the two junctions. Our results a gree with the resent prediction that multiple tunnel attempts of elect ron pairs, which occur when electrons are weakly confined, can add coh erently if the pair consists of nearly time-reversed states. The curre nt modulation results from the dephasing between the corresponding tun nel amplitudes at the two junctions. When the normal wire is covered b y a second superconductor, the conductance is strongly enhanced.