Ultrafast exciton dephasing in semiconducting single-walled carbon nanotubes

Femtosecond two-pulse degenerate four-wave mixing spectroscopy was applied to study the exciton dephasing in a broad range of excitation intensities and lattice temperatures. We find that both exciton-exciton and exciton-phonon scattering have profound effects on the dephasing process. The dominant phonon mode involved in the dephasing is identified as the out-of-plane, transverse optical mode with a frequency of 847cm-1. The extracted homogeneous linewidths at all measured temperatures are in excellent agreement with the results of a single-tube photoluminescence experiment.