Exciton scattering from impurities and acoustic phonons in carbon nanotubes

Exciton scattering from impurities and acoustic phonons in semiconducting carbon nanotubes is theoretically studied in an effective-mass approximation. A selection rule for transitions resulting from the scattering is obtained, showing that the ground-state exciton for the lowest-exciton band is never scattered from long-range impurities and deformation potentials near the band edge. This arises from the symmetry of nanotubes for the successive transformations of the charge conjugation and parity and for the reflection of the coordinate along the nanotube axis. Agreement of numerical results with recent experiments supports the validity of this selection rule