Nearly perfect single-channel conduction in disordered armchair nanoribbons

The low-energy spectrum of graphene nanoribbons with armchair edges (armchair nanoribbons) is described as the superposition of two nonequivalent Dirac points of graphene. In spite of the lack of well-separated two valley structures, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward-scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wave function. For multichannel energy regime, however, the conventional exponential decay of the averaged conductance occurs. Since the intervalley scattering is not completely absent, armchair nanoribbons can be classified into orthogonal universality class irrespective of the range of impurities. The nearly perfect single-channel conduction dominates the low-energy electronic transport in rather narrow nanorribbons.