Coulomb scattering rates of excited carriers in moderate-gap carbon nanotubes

Temperature induces some free carriers in moderate-gap carbon nanotubes, which, thus, creates the low-frequency intraband e-h excitations. Such excitations are the effective deexcitation channels for the excited electrons (holes) in conduction (valence) bands, while they are very weak. The Coulomb decay rates of the lowest two conduction bands are sensitive to the changes in wave vector, radius, and temperature. However, those of the band-edge states depend on chirality weakly. These results directly reflect the strong energy dispersions and the temperature-dependent electron distributions. The calculated results are roughly consistent with the experimental measurements from the ultrafast optical spectroscopies.