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

TL;DR

This paper investigates the two-band Hubbard model using dynamical mean field theory, revealing phase diagrams with spin and orbital freezing phenomena, and discovering a negative-J superconducting phase related to spin-triplet pairing.

Contribution

It provides a comprehensive analysis of phase instabilities in the two-band Hubbard model, including the effects of Hund coupling and anisotropy, and identifies a novel negative-J superconducting phase.

Findings

Negative J leads to intra-orbital spin-singlet superconductivity at low temperatures.

Orbital freezing phenomena characterize the normal state properties.

Phase diagrams depend on Hund coupling and interaction anisotropy.

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.