Metal-semiconductor transition in armchair carbon nanotubes by symmetry breaking

The electronic band structure of armchair carbon nanotubes may be considerably modified by potentials with angular dependence. Different angular modes V _q∼cos qθ have been studied within a tight-binding scheme. Using symmetry arguments, we demonstrate a bandgap opening in these metallic nanotubes when certain selection rules are satisfied for both potential and nanotube structure. We estimate the bandgap opening as a function of both the external potential strength and the nanotube radius and suggest an effective mechanism of metal-semiconductor transition by combination of different forms of perturbations.