Long-range orders, spin- and orbital-freezing in the two-band Hubbard model

Abstract: We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J, an intra-orbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital freezing phenomenon. This is the negative-J analogue of the recently discovered fluctuating-moment induced s-wave spin-triplet superconductivity in the spin-freezing regime of multi-orbital models with J>0.