Spontaneous symmetry breaking in bilayer graphene

Recent experiments [1-4] provided compelling evidence for the correlated electron behavior in undoped bilayer graphene at both zero and finite magnetic field. The key question concerns the nature of the broken-symmetry phases realized experimentally. I will present the phase diagram for the zero-density state in the quantum Hall regime ($\nu=0$ state) obtained within the framerwork of quantum Hall ferromagnetism. Comparing these results with the experimental data of Refs. [1,4], I will argue that the $\nu=0$ insulating state realized in bilayer graphene is the canted antiferromagnetic phase. I will also show that the (canted) antiferromagnetic phase can persist at all magnetic fields down to zero and argue that this is the most likely scenario for the insulating state observed in Ref. [4]. \\[4pt] [1] R. T. Weitz {\em et al.}, Science 330, 812 (2010). \\[0pt] [2] F. Freitag {\em et al.}, arXiv:1104.3816 (2011). \\[0pt] [3] A. S. Mayorov, {\em et al.}, Science 333, 860 (2011). \\[0pt] [4] J. Velasco Jr. {\em et al.}, arXiv:1108.1609 (2011). \\[0pt] [5] M. Kharitonov, arXiv:1103.6285, arXiv:1105.5386, arxiv:1109.1553 (2011).