Low-frequency electronic excitations in doped carbon nanotubes

We study the low-frequency electronic excitations of a doped carbon nanotube. The longitudinal dielectric function, the loss function, and the plasmon frequencies are calculated within the random phase approximation. They strongly depend on the transferred momentum (q), the transferred angular momentum (L), the Fermi energy, and the nanotube geometry (the radius and the chiral angle). All the doped carbon nanotubes could exhibit the L = 0 acoustic plasmon. There also exists the L = 1 optical plasmon, when the Fermi energy is sufficiently high. There are several important differences between type-I nanotubes and type-II nanotubes. The local-field corrections on the loss spectra and the plasmon frequencies are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.