Bilayer graphene has drawn significant attention due to the opening of a band gap in its low energy electronic spectrum, which offers a route to electronic applications that is not practical with single layer graphene. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Our scanning tunneling measurements reveal the microscopic nature of the bilayer gap is very different from the characteristics observed in previous macroscopic measurements or expected from current theoretical models. The band gap, which is proportional to charge imbalance between the layers, shows strong spatial dependence on the disorder potential varying in both magnitude and sign on a microscopic level and is weakly affected by the gate field at small charge densities. We suggest that such gap behavior can be caused by spontaneous symmetry breaking with dipoles nucleated with opposite signs at minima and maxima of the disorder potential.
Citation: Nature Physics
Pub Type: Journals
graphene, bilayer graphene, scanning tunneling microscopy, scanning tunneling spectroscopy, quantum Hall effect