Proximity and anomalous field-effect characteristics in double-wall carbon nanotubes

Proximity effect on field-effect characteristic in double-wall carbon nanotubes is investigated. In a semiconductor-metal double-wall carbon nanotube, the penetration of electron wave functions in the metallic shell to the semiconducting shell turns the original semiconducting shell into a metal where the local density of states is not zero at the Fermi level. By using a two-band tight-binding model on a ladder of two legs, it is demonstrated that anomalous field-effect characteristic in semiconductor-metal-type double-wall carbon nanotubes can be fully understood by the proximity effect of metallic phases.