Quantum-size and nonlinear effects in the plasmonic response of graphene nanoribbons

Graphene nanoribbons provide the means to excite surface plasmon upon direct excitation, avoiding then the momentum mismatch in extended graphene. We describe those collective modes employing a rigorous quantum-mechanical simulation, which accounts for nonlocal, quantum finite-size, and edge-termination effects manifested in the optical response. Our simulations reveal a strong dependence on such phenomena for excitation with a high optical momentum component along the direction of transverse symmetry in both the linear and nonlinear optical response, wherein particular second-order nonlinear phenomena are found to manifest with high efficiency due to the breaking of inversion symmetry. These results can be employed to describe emitters, as two-level atoms, close by used to excite and determine the nonlinear dynamics originated by those plasmons in the graphene nanoribbons.