Abstract Submitted to the NANOTUBE'05 Conference:

Owing to their symmetry and reduced dimensionality, electron-electron Coulomb interaction often strongly influences the behavior of quasi-one-dimensional systems. We show, through first-principles excited-state calculations, that the optical response of carbon nanotubes is qualitatively altered by many-electron interaction effects.[1, 2] It is discovered that exciton states in the semiconducting tubes have binding energies that are orders of magnitude larger than bulk semiconductors and hence they dominate the optical spectrum at all temperature, and that bound excitons can exist even in metallic carbon nanotubes. These predictions demonstrate the crucial importance of an exciton picture in interpreting experimental data. Similar studies show that excitonic effects are even stronger in the BN nanotubes. For both carbon and BN nanotubes, in addition to the optically active (bright) exciton states, theory predicts a number of optically inactive or very weak oscillator strength (dark) exciton states. We have further performed analysis and modeling of the exciton properties (symmetry, binding energy, exciton size, oscillator strength, and radiative lifetime) as a function of factors such as tube diameter, chirality, temperature, and screening due to external medium. The physics behind these phenomena is discussed.

1. C. D. Spataru, S. Ismail-Beigi, L. X. Benedict, and S. G. Louie, Phys. Rev. Lett. 92, 077402 (2004).
2. C. D. Spataru, S. Ismail-Beigi, L. X. Benedict, and S. G. Louie, Appl. Phys. A78, 1129 (2004).

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