Metal-insulator transition, gap opening due to the combined orbital-spin ordering, and spin-triplet superconductivity

Abstract

We consider a metal-insulator transition for the quarter-filled doubly degenerate band of correlated electrons, as well as the onset of the itinerant orbitally ordered phase combined with the saturated ferromagnetism near that limit. The insulating state is instable with respect to either spin-triplet superconductivity or that of ferromagnetic superconductor for strong-enough Hund's-rule coupling. The auxiliary (slave-) boson approach we use reproduces correctly the kinetic-exchange limit for strong correlations.