Theory of a Carbon-Nanotube Polarization Switch

TL;DR

This paper theoretically demonstrates how carrier doping in single-walled carbon nanotubes can reverse their polarization dependence of light absorption, enabling potential use as polarization switches.

Contribution

It specifies the doping level at which polarization anisotropy is reversed and links plasmon excitation to nanotube diameter and doping effects.

Findings

Doping levels can reverse polarization anisotropy in nanotubes.

Plasmon energy depends mainly on nanotube diameter.

Doping affects Coulomb interaction via screened exchange energy.

Abstract

Recently, it was suggested that the polarization dependence of light absorption to a single-walled carbon nanotube is altered by carrier doping. We specify theoretically the doping level at which the polarization anisotropy is reversed by plasmon excitation. The plasmon energy is mainly determined by the diameter of a nanotube, because pseudospin makes the energy independent of the details of the band structure. We find that the effect of doping on the Coulomb interaction appears through the screened exchange energy, which can be observed as changes in the absorption peak positions. Our results strongly suggest the possibility that oriented nanotubes function as a polarization switch.