Photophysics in Single-Walled Carbon Nanotubes with (6,4) Chirality at High Excitation Densities: Bimolecular Auger Recombination and Phase-Space Filling of Excitons

The photophysics in single-walled carbon nanotubes (SWNTs) at high excitation densities has been attracting significant attention for exciton stability. Exciton–exciton interactions and an exciton Mott transition of quasi-one-dimensional excitons in SWNTs are of fundamental interest because the screening effect of the Coulomb interaction is suppressed in one-dimensional systems. In this study, we investigate exciton dynamics and a bimolecular Auger recombination process in SWNTs with (6,4) chirality using femtosecond transient absorption measurements at high excitation densities in the range of 2.4 × 1013–4.8 × 1015 photons cm–2 per pulse. Temporal evolutions of the change in the absorption coefficient are analyzed with an analytical expression for the bimolecular Auger recombination dynamics. We determine the Auger recombination coefficient and initial exciton number per tube, and the absorption cross section is also obtained. By using the phase-space filling model, the exciton size is estimated to be 3.1 ± 1.3 or 2.2 ± 1.0 nm, which depends on the corresponding wave function. Based on the estimated exciton size, the possibility of the Mott transition of quasi-one-dimensional excitons is discussed.