(a) The crystal structure of a bilayer graphene with A₁, A₂, B₁, and B₂ sublattices denoted by white, black, black, and gray circles, respectively, 1 and 2 denote the upper layer and lower layers, a₁, a₂, a₃ are primitive lattice vectors. Solid (dashed) lines denote the nearest neighbour links on the upper (lower) layer. (b) Bilayer graphene with line defects on the upper layer marked by red lines. An electric field is applied perpendicular to the layer (z direction) and the corresponding energy difference between two layers is |2V|.