Coexistence of Spin-Triplet Superconductivity and Ferromagnetism Induced by the Hund’s Rule Exchange

Abstract

We discuss general implications of the local spin-triplet pairing among correlated fermions that is induced by the Hund’s rule coupling in orbitally degenerate systems. The quasiparticle energies, the magnetic moment, and the superconducting gap are determined for the principal superconducting phases, in the situation with the exchange field induced by both the local Coulomb and the Hund’s rule exchange interactions. The phase diagram, as well as the evolution in an applied magnetic field of the spin-triplet paired states near the Stoner threshold, is provided for a model two-band system. The appearance of the spin-polarized superconducting phase makes the Stoner threshold a hidden critical point, since the pairing creates a small but detectable uniform magnetization. The stability of the superconducting state against the ferromagnetism with an alternant orbital ordering appearing in the strong-coupling limit is also discussed.KeywordsPaired StateSuperconducting Coherence LengthSuperconducting FerromagnetSlave BosonDegenerate BandThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.