Bilayer graphene bears an eightfold degeneracy due to spin, valley, and layer symmetry, allowing for a wealth of broken symmetry states induced by magnetic or electric fields, by strain, or even spontaneously by interaction. We study the electrical transport in clean current annealed suspended bilayer graphene. We find two kinds of devices. In bilayers of type $B1$ the eightfold zero-energy Landau level is partially lifted above a threshold field revealing an insulating $\nu =0$ quantum-Hall state at the charge neutrality point. In bilayers of type $B2$ the Landau level lifting is full and a gap appears in the differential conductance even at zero magnetic field, suggesting an insulating spontaneously broken symmetry state. Unlike $B1$, the minimum conductance in $B2$ is not exponentially suppressed, but remains finite with a value $G\lesssim e^2/h$ even in a large magnetic field. We suggest that this phase of $B2$ is insulating in the bulk and bound by compressible edge states.

• Received 23 June 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.076602