Effects of the edge states on conductance and thermopower for the bilayer graphene nanoribbons

Abstract

By using the nonequilibrium Green’s function combined with the tight-binding Hamiltonian, we have studied the effects of the edge states on the conductance and the thermopower for zigzag bilayer graphene nanoribbons (ZBGNs). It is shows that the band structure, conductance, and thermopower can be modulated by the boundary potentials and the bias voltages to the layers of the ZBGNs. When the boundary potentials are adjusted to the nearest neighbor hopping energy, two gapless edge modes with opposite velocities appear in the vicinity of the two Dirac points, and the quantized conductance has a transition from 2(n+1)G0 to 2(n+1/2)G0 with G0=2e2/h being the conductance unit and n an integer. Particularly, under the strong bias voltage, compare to the gapless perfect ZBGN, the thermopower can be enhanced more than twice for the gapless edge modes with opposite velocities. Combining the reduced thermal conductivity in few-layer graphene, our results show that the modulated ZBGNs are more reliable in thermoelectric application.