Electronic properties of carbon nanotubes under external fields

Low-energy electronic properties of carbon nanotubes subject to the influences of a transverse electric field and a magnetic field with angle α are studied by the tight-binding model. The external fields would modulate energy dispersions, alter energy gaps, destroy state degeneracy, and create additional band-edge states. The semiconductor-metal transition is predicted for type-I and type-III nanotubes at all α 's, while it only occurs at certain α 's for type-II nanotubes. The effects of external fields on the band structures are also directly reflected in the density of states (DOS). The numbers, the heights, and the positions of the DOS divergent peaks are strongly dependent on the external fields. Furthermore, the evolution of the DOS peak positions with the electric field strength is also investigated.