The intrinsic transport properties of zigzag graphene nanoribbons (ZGNRs) are
investigated using first principles calculations. It is found that although all
ZGNRs have similar metallic band structure, they show distinctly different
transport behaviors under bias voltages, depending on whether they are mirror
symmetric with respect to the midplane between two edges. Asymmetric ZGNRs
behave as conventional conductors with linear current-voltage dependence, while
symmetric ZGNRs exhibit unexpected very small currents with the presence of a
conductance gap around the Fermi level. This difference is revealed to arise
from different coupling between the conducting subbands around the Fermi level,
which is dependent on the symmetry of the systems.Comment: 4 pages, 4 figure