Biased Bilayer Graphene: Semiconductor with a Gap Tunable by the Electric Field Effect

We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density. We show that the gap can be changed from zero to midinfrared energies by using fields of ≲1V/nm, below the electric breakdown of SiO₂. The opening of a gap is clearly seen in the quantum Hall regime.