Modulation of electronic states in semiconducting carbon-nanotubes with external electrodes

Electronic states are theoretically studied in carbon-nanotubes with external electrodes. To elucidate effects of the electrodes, we examine roles of external modulating potentials. In metallic nanotubes, the potentials hardly affect the energy levels nor envelope functions of the wavefunctions. In semiconducting nanotubes, however, the external potentials significantly influence the electronic states: With increasing the strength of the potentials, the energy gap decreases to zero, whereas the wavefunctions are more localized.