Plasmons in graphene nanoribbons: Interband transitions and nonlocal effects

Abstract

We study plasmon excitations in infinitely long graphene nanoribbons using a quasistatic approach, where one-dimensional coupled equations for electrostatic potential and excited charge density are derived in the transverse direction. By incorporating a hydrodynamical description of the excited charge density, we investigate nonlocal effects in plasmon excitations. Moreover, the method presented here provides means to look into the nonlocal plasmon response in more complex graphene nanostructures such as wedges. We find that the plasmon frequencies are lowered by interband transitions and raised due to nonlocal effects. The frequency shifts depend monotonically on the dielectric constant of the surrounding medium. Most importantly, the nonlocal effects can strongly affect the excited charge density at the edges. Finally, we show that a larger increase of dipolar plasmon frequencies occurs in smaller graphene nanoribbons as expected.