Fermi surface topology and ferromagnetic superconductivity in UGe$_2$

Abstract

We consider a Stoner ferromagnet in presence of a quasi-one dimensional Fermi surface in its spin majority band. Assuming a twin $δ$-function peaked density of state due to the low dimensionality, we computed the single particle self-energy. There appears an additional divergence in the self-energy and hence in the effective mass inside the ferromagnetic phase (besides the standard logarithmic divergence at the Stoner critical point). Since such an effect is purely due to density of states, it might correspond to a first order phase transition making the ferromagnetic phase into two distinct phases. This result is in qualitative agreement with the recent specific heat capacity measurement. We also discuss its relevance to the superconducting state in UGe$_2$.