Intersubband plasmon excitations in doped carbon nanotubes

We theoretically investigate intersubband plasmon excitations in doped single-wall carbon nanotubes (SWNTs) by examining the dependence of plasmon frequency on the nanotube diameter, chirality, and Fermi energy. The intersubband plasmons can be excited by light with polarization perpendicular to the nanotube axis and thus the plasmon excitations correspond to optical transitions between the two different subbands, which are sensitive to the Fermi energy. In every SWNT, this mechanism leads to the emergence of the optical absorption peak at the plasmon frequency for a given Fermi energy, EF. The plasmon frequencies calculated for many SWNTs with diameter dt