Excitons and high-order optical transitions in individual carbon nanotubes

TL;DR

This study investigates the excitonic properties of high-energy optical transitions in individual carbon nanotubes using Rayleigh scattering spectroscopy, revealing excitonic behavior in both semiconducting and metallic types.

Contribution

It provides detailed spectroscopic analysis confirming excitonic nature of high-lying optical transitions in single-walled carbon nanotubes, including identification of exciton-phonon bound states.

Findings

Excitonic lineshape observed in both semiconducting and metallic nanotubes.

Side-bands at ~200 meV indicate exciton-phonon bound states in semiconducting nanotubes.

Metallic nanotubes show no such side-bands, consistent with weaker excitonic interactions.

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 lineshape is consistent with an excitonic model, but not one of free-carriers. For semiconducting species, side-bands are observed at ~200 meV above the third and fourth optical transitions. These features are ascribed to exciton-phonon bound states. Such side-bands are not apparent for metallic nanotubes,as expected from the reduced strength of excitonic interactions in these systems.