Plasmon modes and screening in double metallic armchair graphene nanoribbons

We theoretically study the plasmon modes in double parallel metallic armchair graphene nanoribbons (AGNRs) separated by a distance L_b. Starting with a single doped metallic AGNR at zero temperature, we show the plasmon dispersion dependence on the Fermi wave vector. By evaluating the static dielectric function for this ribbon, we find that the usual logarithmic divergence at q=2k_F is absent. This indicates that plasmons in metallic AGNRs might be the most robust charge-density oscillations occurring in quasi-one-dimensional electron systems. We also study the influence of the distance L_b and of the carrier densities on the out-of-phase and in-phase plasmon modes. Finally, we address the intra-intersubband electron-hole transitions in single metallic armchair ribbons and find a strong influence of doping on the intrasubband plasmon modes.