Boltzmann conductivity of a carbon nanotube in magnetic fields

The magneto conductivity of single-shell carbon nanotubes is calculated in the effective-mass approximation. The conductivity changes sensitively as a function of the Fermi-level position and a magnetic field perpendicular to the tube axis. In the limit of high magnetic fields, the conductivity becomes insensitive to whether the nanotube is metallic or semiconducting and to the presence of a magnetic flux passing through the cross section. Undoped metallic nanotubes exhibit a large positive magnetoresistance in agreement with recent experiments for bundles.