Transport across a normal-superconducting interface: a novel probe of electron-electron interactions in the normal metal

In this letter, we examine the effect of Coulomb interactions in the normal region of a normal-superconducting (N/S) mesoscopic structure; here the change from an attractive to a repulsive Coulombic interaction, at the N/S interface, causes a shift in the order parameter phase. We show that this shift has a pronounced effect on the Andreev bound states and demonstrate that the effect on Andreev scattering of non-zero order parameter tails can be used to probe the sign of the interaction in the normal region.