π-band contribution to the optical properties of carbon nanotubes: Effects of chirality

Abstract

We study the π-band contribution to the optical properties of the carbon nanotubes based on the tight-binding model, including optical absorptions, optical rotatory power, and circular dichroism. By taking into account not only the interband contributions but also the free-carrier contributions, the dielectric functions and the third-rank tensor responsible for the optical activity are calculated. The following have been shown. (i) The features of the dielectric functions are consistent with the ellipsometry experiments by de Heer and co-workers [Science 268, 845 (1995)]; (ii) The calculated plasma frequency is of the same order of magnitude as the one recently observed by Bommeli et al. [Solid State Commun. 99, 513 (1996)]. (iii) Chiral nanotubes are, as expected, optically active and the spectra of their optical rotatory power (RP) and circular dichroism (CD) are highly oscillatory. (iv) Nanotubes with a diameter about 4 nm can give RP and CD that are of the same order of magnitude as those of certain organic compounds. (v) The RP and CD decrease as the diameter increases.