Disorder enhanced conductance in graphene

We study the effect of short-range disorder on the localization property of the electronic state in zigzag graphene, via the calculation of the two-terminal dc conductance with the transfer matrix method. When the disorder is weak, the electron states are localized. However, when the disorder crosses the critical strength, the conductance will be enhanced and may be even quantized as e2/h at the specific disorder strength. Our numerical calculations suggest that the quantized conductance shows certain robustness to the system size, shape and the Fermi energy. We demonstrate the unconventional behavior from the localization length and the density of states and attribute it to the existence of edge states. The implications of our results are discussed.