A sheet of carbon just one atom thick is placed in a strong magnetic field and cooled to thousandths of a degree above absolute zero. A microwave microscope slides along the sheet's edge, measuring how well that edge conducts electricity. At neutral charge, when electrons and holes are equal in number, the edge behaves differently from the sheet's middle.

As the magnetic field increases, conductivity in the center of graphene drops to zero faster than at the edge. Calculations show that under these conditions, a 'canted' antiferromagnetic phase emerges in graphene, where electron spins align in a special way. It is this phase that creates an energy gap at the edge, a forbidden zone for electrons, distinct from that in the bulk.

For comparison, the researchers measured the graphene edge in states with integer quantum filling, where lossless currents flow along the edge. There, the picture is fundamentally different: the edge remains conducting while the bulk has a gap. The difference between zero and nonzero filling is explained by numerical simulations and theory.

These observations provide a complete microscopic picture of how edge and bulk states change as the Fermi level moves through graphene's unique Landau level spectrum. Understanding such edges is important for future devices based on topological states and quantum technologies.