Edge effects on quantum thermal transport in graphene nanoribbons: Tight-binding calculations

We investigate the quantum thermal transport properties of graphene nanoribbons (GNRs) with natural edges by combining the Naval Research Laboratory tight-binding approach and the phonon nonequilibrium Green's function method. Thermal transport of GNRs shows substantial dependence on the width due to edge reconstructions. For GNRs with n >= 12, where n is the number of atoms along the direction perpendicular to the ribbon axis, the effect of natural edges is negligible and quantized thermal transport is observed. For GNRs with 2 < n < 12, natural edges destroy quantized thermal transport and reduce thermal conductance significantly. For the narrowest GNR with n=2, perfect quantized thermal transport is restored and a zero-transmission phonon band gap appears at omega=785 similar to 808 cm(-1). By sandwiching the narrowest GNR between two wide GNRs, the band gap is broadened by about ten times. The thermal conductivity of graphene evaluated from our results agrees very well with the recent experimental measurements.