LATTICE DISTORTION OF METALLIC CARBON NANOTUBES INDUCED BY MAGNETIC-FIELDS

A lattice instability toward in-plane Kekule and out-of-plane distortions is studied for metallic carbon nanotubes in a magnetic field perpendicular to the tube axis using a k.p approximation. A strong magnetic field drastically enhances the distortion for the nanotubes with larger circumference and leads to a gap almost independent of an Aharonov-Bohm magnetic flux passing through the cross section. For the Kekule distortion, in particular, the gap increases with the circumference length and approaches a value smaller than that of a 2D graphite sheet by a factor of 2/pi.