Interactions of fast ions with carbon nanotubes: Two-fluid model

We propose a simple, parameter-free two-fluid model for the collective electron response of a single-walled carbon nanotube, which treats the sigma and pi electrons as separate two-dimensional fluids constrained to the same cylindrical surface. The electrostatic interaction between the fluids gives rise to splitting of the plasmon frequencies into two groups closely following the experimentally determined longitudinal dispersions of the sigma+pi and pi plasmons. The model is used to calculate the induced electron density on the nanotube, as well as the stopping power for a charged particle moving parallel to the axis of the nanotube. It is found that these quantities exhibit novel features when the particle speed matches the phase velocity of the quasiacoustic pi plasmon.