Kohn-Luttinger superconductivity in the presence of feedback effects

The Kohn-Luttinger scheme is a well known theoretical mechanism for deriving superconductivity from repulsive interactions. This has been shown to give rise to attractive Cooper pairing correlations through screening effects, arising from various mechanisms including Kohn anomalies, van Hove electronic structures, and Umklapp scattering effects.

In such instances where the pairing is known to be driven by repulsive interactions (in particular in superfluid He-3), it has been argued that the screening response should incorporate a feedback effect in which the existence of a pairing gap modifies the response functions which are themselves responsible for the pairing attraction. The feedback effects will manifest in strong-pairing superconductors whenever there are substantial preformed Cooper pairs in the normal state.

In this talk we address the question of whether these feedback effects are harmful or helpful for Kohn-Luttinger type of superconductivity. What can be

anticipated is that the presence of a normal state gap may substantially alter the effects of van Hove contributions and Kohn anomalies in Kohn-Luttinger superconductivity.