Ferromagnetism and antiferromagnetism of a correlated topological insulator with a flat band

In this paper, based on the mean-field approach and random-phase approximation, we studied the magnetic properties of the spinfull Haldane model on honeycomb lattice of topological flat band with onsite repulsive Coulomb interaction. We found that the antiferromagnetic (AF) order is more stable than the ferromagnetic (FM) order at, or near, half filling. Away from half filling, the phase diagram becomes complex: at large doping, the FM order is more stable than the AF order due to the flatness of band structure. In particular, we found that at quarter filling, the system becomes a Chern number Q = 1 topological insulator induced by the FM order. DOI:10.1103/PhysRevB.86.235146