Abstract

The electron transport properties with the relativistic intrinsic and Rashba spin-orbit (SO) couplings in a graphene nanoribbon are investigated by using the third-nearest-neighbor tight-binding model and the nonequilibrium Green function method. The numerical results display a perfect quantum spin Hall state (QSH) surrounded by a simple insulator state, presented in Rashba SO coupling vs sublattice potential plane. The QSH state is enhanced by the intrinsic SO coupling, indicating a quantum topological property of graphene nanoribbons.