Non-interacting and interacting Graphene in a strong uniform magnetic field*

We study monolayer graphene in a uniform magnetic field in the absence and presence of interactions. In the non-interacting limit for p/q flux quanta per unit cell, the central two bands have 2q Dirac points in the Brillouin zone in the nearest-neighbor model. These touchings and their locations are guaranteed by chiral symmetry and the lattice symmetries of the honeycomb structure. If we add a staggered potential and a next nearest neighbor hopping we find their competition leads to a topological phase transition. We also study the stability of the Dirac touchings to one-body perturbations that explicitly lowers the symmetry.

In the interacting case, we study the phases in the strong magnetic field limit. We consider on-site Hubbard and nearest-neighbor Heisenberg interactions. In the continuum limit, the theory has been studied before [1]. It has been found that there are four competing phases namely, ferromagnetic, antiferromagnetic, charge density wave, and Kekulé distorted phases. We find phase diagrams for q=3,4,5,6,9,12 where some of the phases found in the continuum limit are co-existent in the lattice limit with some phases not present in the continuum limit.

[1] M. Kharitonov PRB 85, 155439 (2012)