We will present brief overview on the electronic and transport properties of
graphene nanoribbons focusing on the effect of edge shapes and impurity
scattering. The low-energy electronic states of graphene have two
non-equivalent massless Dirac spectrum. The relative distance between these two
Dirac points in the momentum space and edge states due to the existence of the
zigzag type graphene edges are decisive to the electronic and transport
properties of graphene nanoribbons. In graphene nanoribbons with zigzag edges,
two valleys related to each Dirac spectrum are well separated in momentum
space. The propagating modes in each valley contain a single chiral mode
originating from a partially flat band at band center. This feature gives rise
to a perfectly conducting channel in the disordered system, if the impurity
scattering does not connect the two valleys, i.e. for long-range impurity
potentials. On the other hand, the low-energy spectrum of graphene nanoribbons
with armchair edges is described as the superposition of two non-equivalent
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
wavefunction. Symmetry considerations lead to the classification of disordered
zigzag ribbons into the unitary class for long-range impurities, and the
orthogonal class for short-range impurities. However, no such crossover occurs
in armchair nanoribbons
