Exciton-phonon effects in carbon nanotube optical absorption

TL;DR

This paper demonstrates that exciton-phonon interactions significantly influence the optical absorption spectra of carbon nanotubes, revealing a distinct sideband and long-range structural distortions dependent on chirality.

Contribution

It provides the first detailed analysis of exciton-phonon coupling effects on the optical properties of carbon nanotubes using tight-binding calculations.

Findings

Identification of a prominent exciton+phonon sideband at 200 meV above the main peak

Quantification of exciton-phonon coupling leading to a binding energy up to 100 meV

Discovery of long-range, chirality-dependent structural distortions

Abstract

We find that the optical properties of carbon nanotubes reflect remarkably strong effects of exciton-phonon coupling. Tight-binding calculations show that a significant fraction of the spectral weight of the absorption peak is transferred to a distinct exciton+phonon sideband, which is peaked at around 200 meV above the main absorption peak. This sideband provides a distinctive signature of the excitonic character of the optical transition. The exciton-phonon coupling is reflected in a dynamical structural distortion, which contributes a binding energy of up to 100 meV. The distortion is surprisingly long-ranged, and is strongly dependent on chirality.