Excitation-induced dephasing and ultrafast intrasubband relaxation in carbon nanotubes

We present theoretical investigations of the ultrafast relaxation dynamics and the excitation-induced dephasing of excitonic polarization in single-walled carbon nanotubes. Our microscopic approach is based on the density-matrix theory combined with tight-binding wave functions allowing the calculation of tubes with arbitrary diameter and chiral angle. For excitations to the single-particle continuum, the initial nonequilibrium carrier distribution is thermalized within approximately 100 fs while the polarization adiabatically follows the excitation pulse. For excitations at the excitonic resonance, we find a dephasing of the excitonic polarization on a picosecond time scale depending on the excitation strength. With increasing field intensities, the dephasing time linearly decreases, which is in agreement with recent experiments.