Electric field effects on the energy spectrum of carbon nanotubes

Electronic properties of straight carbon nanotubes under an external electric are investigated, following a single-π-orbital tight binding approximation. Metal-insulator transitions in metallic tubes and energy gap modulations in semiconducting ones were found due to the action of the electric field. Reductions in the tube symmetry operations induced by the field are manifested in the energy spectrum as a function of the angle determined by the field direction and equivalent in-plane atomic positions along the circumferential direction. We find that particular energies in the spectra exhibit a periodic oscillation with this dephasing angle. The range and position of those energies, as well the amplitude of the oscillation, can be properly manipulated by changing the strength and direction of the applied electric field.