Spin triplet superconductivity driven by finite momentum spin fluctuations

A small number of superconductors are believed to exhibit intrinsic spin triplet pairing,

and are often discussed in terms of a simple, ³He-like picture where ferromagnetic spin

fluctuations provide the "glue".  However, in some cases where reliable inelastic neutron

scattering measurements are available, spin excitations are found to be peaked at finite

momentum rather than at q=0. Here we investigate some simple models that exhibit

triplet pairing arising from antiferromagnetic spin fluctuations. We show that a strong

peak at larger momentum in the magnetic susceptibility can drive such states,

typically leading to additional nodes in the gap function. In these situations,  dominant pair

scattering processes occur between Fermi surface segments with like signs of the

superconducting order parameter, yet are consistent with an overall odd parity state.

We examine the applicability of these scenarios to the putative triplet superconductor

UTe₂ by calculations based on three dimensional Fermi surfaces.