Pairing in 3D fermions with repulsive and non-local interactions: A tractable crossing-symmetric approach

Recent discoveries of superconductivity in novel strongly interacting systems and the prospect of unconventional pairing have generated great interest. We study general nature of pairing in strongly interacting 3D Fermi systems, with underlying repulsive and non-local interactions, using a diagrammatic crossing-symmetric equations method. This allows for the treating of competing density, spin, and current fluctuations in a self-consistent fashion, resulting in renormalized Fermi liquid interactions and, therefrom, obtaining pairing amplitudes in different angular momentum channels (viz. s, p, d). While repulsive interactions result in non-s-wave pairing, non-local interactions play important role in enhancing certain quantum fluctuations and determining the pairing symmetry, namely, switching from p-wave to s-wave pairing for sufficiently repulsive non-local interaction; and to a narrow region of d-wave pairing in the attractive case. The s-wave pairing is driven by transverse current fluctuations competing with ferromagnetic spin fluctuations, and the d-wave pairing by antiferromagnetic-like spin fluctuations.