  Electrostatic screening between carbon nanotubes (CNTs) in a small CNT bundle
leads to a switching behavior induced by electric field perpendicular to the
bundle axis. Using a first-principles method, we investigate the electronic
structures of bundles consisting of two or three CNTs and the effects of the
electric field applied perpendicular to the bundle axis. The applied field
causes band gap closure in semiconducting bundles, while a gap opening occurs
in metallic ones, which enables considerable modulation of bundle conductivity.
The modulation effect originates from symmetry breaking due to electrostatic
screening between the adjacent tube walls.
