Semiconductor-metal and metal-semiconductor transitions in twisting graphene nanoribbons

The electronic structure and transport properties of twisting graphene nanoribbons (TGNRs) are systematically investigated using the tight-binding model and the non-equilibrium Green's function method. We show that the energy gap and conductance around the Fermi energy can be reversibly modulated. Armchair TGNRs (ATGNRs) can be either metallic or semiconducting depending on the widths and the twist angles of the GNRs. Semiconductor-metal and metal-semiconductor transitions are observed in ATGNRs for N=3i+1 (where i is an integer and N is the number of atoms along the width of the nanoribbon) and N=3i+2, respectively. Narrow ATGNRs are semiconductors for N=3i, whereas zigzag TGNRs (ZTGNRs) are metallic regardless of the width and distortion of the GNRs.