Topological Phase Transitions in the Repulsively Interacting Haldane-Hubbard Model

Using dynamical mean-field theory and exact diagonalization we study the phase diagram of the repulsive Haldane-Hubbard model, varying the interaction strength and the sublattice potential difference. In addition to the quantum Hall phase with Chern number C = 2 and the band insulator with C = 0 present already in the noninteracting model, the system also exhibits a C = 0 Mott insulating phase, and a C = 1 quantum Hall phase. We explain the latter phase by a spontaneous symmetry breaking where one of the spin components is in the Hall state and the other in the band insulating state.