Electronic structure and dynamics of optically excited single-wall carbon nanotubes

TL;DR

This study investigates the electronic properties and charge-carrier dynamics of individual single-wall carbon nanotubes using optical and spectroscopic techniques, revealing insights into their energy transitions, decay processes, and electron-phonon interactions.

Contribution

It provides a semi-empirical model for transition energies and detailed measurements of ultrafast carrier dynamics in SWNTs, advancing understanding of their electronic behavior.

Findings

Semi-empirical expression matches experimental transition energies.

Charge-carrier decay time is approximately 15 ps.

Electron-phonon coupling in metallic tubes is very weak.

Abstract

We have studied the electronic structure and charge-carrier dynamics of individual single-wall carbon nanotubes (SWNTs) and nanotube ropes using optical and electron-spectroscopic techniques. The electronic structure of semiconducting SWNTs in the band-gap region is analyzed using near-infrared absorption spectroscopy. A semi-empirical expression for $E_{11}^{\rm S}$ transition energies, based on tight-binding calculations is found to give striking agreement with experimental data. Time-resolved PL from dispersed SWNT-micelles shows a decay with a time constant of about 15 ps. Using time-resolved photoemission we also find that the electron-phonon ({\it e-ph}) coupling in metallic tubes is characterized by a very small {\it e-ph} mass-enhancement of 0.0004. Ultrafast electron-electron scattering of photo-excited carriers in nanotube ropes is finally found to lead to internal thermalization of the electronic system within about 200 fs.