Excitons and high-order optical transitions in individual carbon nanotubes: A Rayleigh scattering spectroscopy study

Abstract

We examine the excitonic nature of high-lying optical transitions in single-walled carbon nanotubes by means of Rayleigh scattering spectroscopy. A careful analysis of the principal transitions of individual semiconducting and metallic nanotubes reveals that in both cases the line shape is consistent with an excitonic model, but not one of free carriers. For semiconducting species, sidebands are observed at $\ensuremath{\sim}200\text{ }\text{meV}$ above the third and fourth optical transitions. These features are ascribed to exciton-phonon bound states. Such sidebands are not apparent for metallic nanotubes, as expected from the reduced strength of excitonic interactions in these systems.