Plasmons and excitons in graphene nanoribbons: A comparative study with carbon nanotubes Graphene nanoribbons are quasi-one-dimensional graphnene. We study excitons and plasmons in graphene nanoribbons comparing with those in carbon nanotubes. Figures show calculated optical absorption spectra of a semiconducting armchair graphene nanoribbon, which show absorption peaks arising from (a) excitons, (b) plasmons for interband transitions, and (c) plasmons for intraband transitions. When units of energy of horizontal axes are appropriately chosen, energies of these peaks approximately agree with those for carbon nanotubes. This is due to the fact that energy bands of graphene nanoribbons are same as those of carbon nanotubes when energy and wave vectors are scaled in an appropriate manner. Calculated optical absorption spectra of a graphene nanoribbon (red lines) and carbon nanotubes (blue lines). The width of the graphene nanoribbon is chosen as W=5.5 nm and the circumferences of carbon nanotubes are L=W/2 and W. (a) shows absorption peaks caused by excitons without carrier doping, (b) shows absorption peaks caused by plasmons for interband transitions with carrier doping where the Fermi energy crosses the second bands, and (c) shows absorption peaks caused by plasmons for intraband transitions with carrier doping where the Fermi energy crosses the first bands. Reference S. Uryu, Phys. Rev. B 102, 155409 (2020). Back
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