Spin Versus Charge Density Wave Order in Graphene-like Systems
  A variational technique is used to study sublattice symmetry breaking by strong on-site and nearest neighbor interactions in graphene. When interactions are strong enough to break sublattice symmetry, and with relative strengths characteristic of graphene, a charge density wave Mott insulator is favored over the spin density wave condensates. In the spin density wave condensate we find that introduction of a staggered on-site energy (quasiparticle mass) leads to a splitting of the fermi velocities and mass gaps of the quasiparticle spin states. 
Y. Araki and G. W. Semenoff
cond-mat.str-el cond-mat.mes-hall hep-th