Exciton absorption of perpendicularly polarized light in carbon nanotubes

Optical absorption in carbon nanotubes for polarization perpendicular to the tube axis is studied taking account of exciton effects. Although a strong depolarization effect tends to shift the position to the higher energy side and suppress the intensity, excitons manifest themselves as prominent peaks because of their large binding energy. The resulting absorption energy is closer to that associated with that of the second gap for light polarized parallel to the axis.