Coexistence of strong pairing correlations and itinerant ferromagnetism arising from spin asymmetric bandwidths: A reduced BCS model study

We investigate the conditions for the occurrence of the coexisting phases that exhibit singlet superconductivity and itinerant ferromagnetism arising from spin asymmetric bandwidths. The exact solution for a reduced BCS pairing model with spin dependent bandwidths is used to determine the ground-state diagram as a function of the coupling parameter, the total density, and the topology of the single-particle spectrum. A spin-polarized superconducting state is obtained in the regime of large pair couplings with a strong bandwidth asymmetry. The analysis reveals that, for such a type of ferromagnetism, small (large) values of the density of states at energies close to the edges of the band enhance (hinder) the tendency toward a coexistence of strong pairing correlations and finite spin polarizations.