Berry's Phase and Absence of Back Scattering in Carbon Nanotubes

The absence of back scattering in carbon nanotubes is shown to be ascribed to Berry's phase which corresponds to a sign change of the wave function under a spin rotation of a neutrino-like particle in a two-dimensional graphite. Effects of trigonal warping of the bands appearing in a higher order k · p approximation are shown to give rise to a small probability of back scattering.