Tunneling Spectroscopy in Strongly Interacting Superconductors

We study tunnelling conductance across a normal metal-superconducting (N-S) junction for a strongly interacting superconductor across a BCS-BEC crossover using non-equilibrium field theory. We show that an energy dependent microscopic coupling between the metal and superconductor is crucial to obtain the correct ballistic limit. For an s-wave superconductor, we find that the weak barrier Andreev tunnelling spectroscopically tracks the single particle gap, rather than the superconducting order parameter. The zero bias Andreev conductance decreases monotonically with increasing interactions.