Electronic energy band structures of carbon nanotubes with spin-orbit coupling interaction

Based on the symmetry adapted tight-binding model, the electronic energy band structures of single wall carbon nanotubes are calculated by considering the spin-orbit coupling interaction. The energy gaps at the Dirac point for the armchair nanotubes are formed due to the spin-orbit coupling interaction and the curvature effect. For the zigzag and chiral carbon nanotubes, the energy band splittings for the lowest unoccupied states and the highest occupied states are also formed by the spin-orbit coupling interaction. The energy splittings are not only dependedent on the diameter and the chiral angle of the carbon nanotubes, but also a symmetric with respect to the Fermi energy level. According to the chiral index (n, m), different tube behaviors are grouped into three families. The numeral results are in good agreement with the experimental results.