Hund's rule coupling as the microscopic origin of the spin-triplet pairing in a correlated and degenerate band system

Abstract

We propose that the spin-triplet pairing can originate from the intraatomic Hund's rule exchange in a degenerate d-band system. The role of this interaction in the pairing is decisive when accounted for in conjunction with rather strong correlations induced by the direct Coulomb interactions. The superconducting-gap value is obtained in the saddle-point approximation for the Coulomb correlations, treated in the auxiliary Bose field approach, which is combined with the mean-field approximation of the BCS type for the pairing part.