Plasmon properties of doped or gated graphene nanoribbon arrays with armchair shaped edges

The exceptional ability to manipulate the electromagnetic response of two-dimensional graphene-like structures at the nanoscale, due to plasmon excitations, has paved the way for new challenges in electronics and photonics. Practical applications have stressed the key role played by the edges of the nanomaterials, which generate peculiar plasmon modes interfering with the usual bulk or surface modes of the ideal (infinitely extended) systems. In particular, recent spectacular experiments have cast light into the spatial dispersion of confined plasmon oscillations in graphene nanoribbon arrays, detecting and resolving a onedimensional (edge) mode from a two-dimensional (surface) mode. On the theoretical side, a number of semi-phenomenological and parameter-dependent approaches have been able to catch the main features of the plasmon response from diverse types of nanoribbon structures, explicitly including edge-roughness effects. Nonetheless, current synthesized nanoribbon sizes have made it possible to test more self-consistent atomistic strategies, based on time-dependent density functional theory. Recently, some noteworthy ab initio calculations of this type have shown how edge and surface plasmon modes are generated and interact in the narrowest nanoribbon arrays (1 nm wide). The shape and dispersion of these modes have been simulated by a probe particle (electron or photon) with incident momentum parallel to the ribbon axis. Here, we extend these previous results and investigate how the interplay of edge and surface plasmons is modulated by the ribbon width, in a range of 0.7 to 3 nm. We thus suggest and recommend using density functional theory based methods to extend current views on the plasmonics of low dimensional materials.