Optical dichroism in nanotubes

Utilizing the line-group symmetry of single-wall nanotubes, we have assigned their electron-energy bands by symmetry-based quantum numbers. The selection rules for optical absorption are presented in terms of these quantum numbers. Different interband transitions become allowed as the polarization of incident light is varied, and we predict a substantial optical dichroism. We suggest how to observe this effect in experiments on a single nanotube, and how it can be used to control quantum transport in nanotubes to obtain information about the structure.