π-electronic excitations in multiwalled carbon nanotubes

The π-electronic excitations of the 3D (2D) multiwalled carbon nanotube bundles (arrays) are studied within the linear response approximation. The longitudinal dielectric function exhibits a peak or diplike structure at the neighborhood of ω = 2γ₀ (γ₀ is the resonance integral). This special structure induces a pronounced π-plasmon peak in the loss function. The π-plasmon frequency and the oscillator strength of collective excitations are significantly affected by the direction and the magnitude of the transferred momentum, the number of shells in a multiwalled nanotube, and the dimensionalities of the coupled multiwalled nanotube systems. On the other hand, they are insensitive to the electronic structure of the single-walled carbon nanotube (or the chiral angle) and the slight change of the shell number. The predicted π-plasmon characteristics could be experimentally checked with EELS or optical spectra.