Exciton effects in optical absorption spectra of boron-nitride (BN) nanotubes

TL;DR

This paper investigates exciton effects in boron-nitride nanotubes, analyzing how Coulomb interactions influence their optical properties and revealing their independence from nanotube geometry, unlike carbon nanotubes.

Contribution

It provides a detailed theoretical analysis of exciton effects in BN nanotubes, highlighting their unique independence from geometric variations.

Findings

Optical gap of (5,0) BN nanotube is about 6 eV.

Exciton binding energy is approximately 0.50 eV.

Energy gap and binding energy are nearly independent of nanotube geometry.

Abstract

Exciton effects are studied in single-wall boron-nitride nanotubes. The Coulomb interaction dependence of the band gap, the optical gap, and the binding energy of excitons are discussed. The optical gap of the (5,0) nanotube is about 6eV at the onsite interaction U=2t with the hopping integral t=1.1eV. The binding energy of the exciton is 0.50eV for these parameters. This energy agrees well with that of other theoretical investigations. We find that the energy gap and the binding energy are almost independent of the geometries of nanotubes. This novel property is in contrast with that of the carbon nanotubes which show metallic and semiconducting properties depending on the chiralities.