A simple slave-boson representation combined with the Hartree-Fock approximation for the Hund's rule coupling is introduced for a doubly degenerate narrow band, which bears a direct relation to that introduced previously in the nondegenerate case. Namely, one keeps the fermion representation of the spin operator to recover properly the energy of fermionic quasiparticles in the presence of an applied magnetic field. A simple two-parameter mean-field analysis of the metamagnetism is provided, with the emphasis on the role of the Hund's rule coupling. We also analyse the appearance of the spin-split effective masses in the applied field and for nonhalf-filled-band situation. The Mott-Hubbard boundary is determined at nonzero temperature (T > 0); it shifts towards lower interactions with increasing T and the field signalling the precursory localization effects, explicitly exhibited in the behavior of the magnetic susceptibility calculated in the Appendix. We also formulate a more general two-parameter rotationally invariant approach for an arbitrary degeneracy d of equivalent orbitals and show that the Mott-Hubbard transition at zero temperature and at any integer filling n > 1 is always discontinuous. A brief overview of experimental situation is also made.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.