Novel Magnetic Properties of Carbon Nanotubes

An external magnetic field is found to have strong effects on the electronic structure of carbon nanotubes. A field-induced metal-insulator transition is predicted for all pure nanotubes. In a weak field, nanotubes exhibit both large diamagnetic and paramagnetic responses which depend on the field direction, the position of the Fermi energy, the helicity, and the size of the nanotube. Universal scalings are found for the susceptibility as functions of the Fermi energy, the temperature, and the size of nanotubes. These results are in agreement with experiments.