Presence of perfectly conducting channel in metallic carbon nanotubes

It is proved that a conducting channel transmitting perfectly without backscattering is present independent of energy in metallic carbon nanotubes for scatterers with potential range larger than the lattice constant. In the case that several traveling channels are present, the conductance decreases from the ideal value determined by the number of traveling modes to the single-channel value when the length exceeds the mean free path determined by a Boltzmann transport equation. Further, inelastic scattering makes the conductance decrease in proportion to the inverse of the length in qualitative agreement with the Boltzmann result.