Field modulation in bilayer graphene band structure.

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-[Formula: see text] symmetry. We analyze strain effects on the bilayer graphene using the extended Hückel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 Å interlayer distance, the band gap is direct, follows a convex relation with the electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 Å, the band gap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.