Uniform Peak Optical Conductivity in Single-Walled Carbon Nanotubes

TL;DR

This paper explains why single-walled carbon nanotubes exhibit a universal peak optical conductivity of about 8 e^2/h, linking it to their relativistic band structure and Coulomb interactions, and provides a predictive exciton model.

Contribution

It introduces a minimalist exciton dynamics model that accurately predicts the uniform peak optical conductivity in carbon nanotubes, highlighting the role of relativistic band structure.

Findings

Peak optical conductivity is approximately 8 e^2/h for all nanotubes.

The uniformity arises from relativistic band structure and Coulomb interactions.

The model accurately predicts the numerical value of the peak conductivity.

Abstract

Recent measurements in single-walled carbon nanotubes show that, on resonance, all nanotubes display the same peak optical conductivity of approximately 8 $e^2/h$, independent of radius or chirality [Joh \emph{et al.}, \emph{Nature Nanotechnology} \textbf{6}, 51 (2011)]. We show that this uniform peak conductivity is a consequence of the relativistic band structure and strength of the Coulomb interaction in carbon nanotubes. We further construct a minimalist model of exciton dynamics that describes the general phenomenology and provides an accurate prediction of the numerical value of the peak optical conductivity. The work illustrates the need for careful treatment of relaxation mechanisms in modeling the optoelectronic properties of carbon nanotubes.