Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes

TL;DR

This study investigates Fano resonances in the mid-infrared spectra of single-walled carbon nanotubes, revealing asymmetric phonon lineshapes and enhanced cross-sections upon doping, linked to electron-phonon interactions.

Contribution

It demonstrates the presence of Fano resonances in carbon nanotubes and relates these to doping and defect-induced effects on phonon-electron coupling.

Findings

Phonon bands exhibit asymmetric lineshapes.

Doping enhances the phonon cross-section.

Defects increase resonance probabilities.

Abstract

This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the resonance probabilities.