Theory of intraband plasmons in doped carbon nanotubes: rolled surface-plasmons of graphene

TL;DR

This paper investigates how heavy doping in single-wall carbon nanotubes induces intraband plasmons, revealing new resonance features in the near-infrared and terahertz regions linked to azimuthal and axial plasmons.

Contribution

It demonstrates the emergence of intraband plasmons in doped nanotubes and clarifies their spectral signatures, expanding understanding of plasmon behavior in these nanostructures.

Findings

Heavy doping induces azimuthal plasmons as near-infrared resonances.

Axial plasmons contribute to terahertz absorption peaks.

Polarization controls excitation of different plasmon modes.

Abstract

A single-wall carbon nanotube possesses two different types of plasmons specified by the wavenumbers in the azimuthal and axial directions. The azimuthal plasmon that is caused by interband transitions has been studied, while the effect of charge doping is unknown. In this paper, we show that when nanotubes are heavily doped, intraband transitions cause the azimuthal plasmons to appear as a plasmon resonance in the near-infrared region of the absorption spectra, which is absent for light doping due to the screening effect. The axial plasmons that are inherent in the cylindrical waveguide structures of nanotubes, account for the absorption peak of the metallic nanotube observed in the terahertz region. The excitation of axial (azimuthal) plasmons requires a linearly polarized light parallel (perpendicular) to the tube's axis.