Exciton transport and manipulation in colloidal semiconducting carbon nanotubes

Exciton transport in carbon nanotubes is determined by the group velocity of the bound electron-hole pair wavepacket and dephasing scattering mechanisms such as exciton-phonon coupling. The electron-hole exchange interaction in small diameter semiconducting carbon nanotubes leads to an anomalous exciton dispersion that renormalizes the exciton effective mass with respect to the free-particle picture. This results in rather large group velocities approaching 1 nm/fs. However, in a colloidal environment we found that coherence lengths are limited to the exciton size, and the intrinsic exciton diffusion constant associated with acoustic phonon scattering is reduced by a factor of 40 to ~ 7.5 cm²/s. We associate this reduction in diffusion constant to exciton scattering within a disorder potential associated with the dynamic colloidal interface. I will also present evidence of strong exciton-plasmon coupling when nanotubes are in proximity to sharp metal tips and edges associated with ultra-smooth (<1 nm RMS surface roughness) gold-pyramid substrates. Propagating and emitting surface plasmon polaritons at the nanotube emission wavelengths, bright localized exciton emission, and a reorientation of the exciton dipole moment all provide evidence for this coupling.