We report on transport measurements of the insulating state that forms at the charge neutrality point of graphene in a magnetic field. Using both conventional two-terminal measurements, sensitive to bulk and edge conductance, and Corbino measurements, sensitive only to the bulk conductance, we observed a vanishing conductance with increasing magnetic fields. By examining the resistance changes of this insulating state with varying perpendicular and in-plane fields, we probe the spin-active components of the excitations in total fields of up to 45 T. Our results indicate that the $\nu =0$ quantum Hall state in single layer graphene is not spin-polarized.

• Received 17 November 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.106804