Low-frequency excitation spectra in double-walled armchair carbon nanotubes

The low-frequency electronic excitations of the double-walled armchair carbon nanotubes are investigated by the random-phase approximation. Both the intertube atomic hoppings and the intertube e-e interactions are included in the calculations simultaneously. The intertube atomic hoppings significantly alter the low-energy bands and thus enrich the low-frequency excitation spectra. There are more single-particle excitation channels and plasmon modes. These excitations strongly depend on the symmetric configurations of the double-walled system and the transferred momentum, such as the number, the existence, the strength, and the frequency of plasmon modes.