Two graphene monolayers that are oppositely charged and placed close to each other are considered. Taking into account valley and spin degeneracy of electrons we analyze the symmetry of the excitonic insulator states in such a system and build a phase diagram that takes into account the effect of the symmetry breaking due to the external in-plane magnetic field and the carrier density imbalance between the layers.
@article{arxiv.1206.5646,
title = {Phases of the excitonic condensate in two-layer graphene},
author = {Yevhen F. Suprunenko and Vadim Cheianov and Vladimir I. Fal'ko},
journal= {arXiv preprint arXiv:1206.5646},
year = {2012}
}