We demonstrated that edge states can be generated by an edge-potential at an armchair-graphene open boundary. The edge states are shown not of the same physical origin as the Tamm states in semiconductors. Pseudospin flipping is found to be the key process leading to the formation of these edge states. At an open boundary, the edge potential is shown to turn on pseudospin-flipped (intravalley) scattering even though there is no obvious breaking of the AB site (basis atoms) symmetry. For a valley-polarized incident beam, the interference between the pseudospin-conserving (intervalley) and nonconserving (intravalley) processes lead to a finite out-of-plane pseudospin density. This same mechanism leads to the edge state formation in the evanescent regime. Discussion will also cover armchair-graphene nanoribbon on the energy gap opening and the conductance.
Ref.  C.H. Chiu and C.S. Chu, Phys. Rev. B 85, 155444 (2012)