Exciton ground state bleaching in (6,5) single walled carbon nanotubes

We model the optical absorption of single walled carbon nanotubes using the quantum Boltzmann equation.

We explore a wide range of initial conditions and determine the dependency of the absorption spectrum as a function of the exciton and phonon populations.

Specifically, we investigate the behaviour of the dominant excitonic peak and the phonon side-bands arising from exciton-phonon coupling.

We observe two distinct behaviours depending on the excitonic statistics.

At low occupancy (i.e. bosonic excitons) there is little to no change in the absorption spectrum.

On the other hand, at high occupancy (i.e. fermionic excitons) we observe an important weakening of both the main excitonic peak and the phonon side-bands.

Most importantly, we observe a "negative" absorption corresponding to the emission of light caused by an excitonic population-inversion effect.

This effect is cause by a Pauli blocking mechanism which is responsible for the bleaching effect observed in many pump-probe experiments.