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One-dimensional characters of excitons in carbon nanotubes

Recent theoretical studies on exciton absorption in carbon nanotubes in an effective-mass approximation are reviewed. It is clarified that one-dimensional character plays important roles in optical properties of carbon nanotubes. For semiconducting tubes, exciton effects for polarization perpendicular to the tube axis cause prominent peaks in optical absorption spectra in spite of the depolarization effect. Calculated excited exciton energies for parallel polarization well reproduce measured energies for one- and two-photon absorption. Excitons can also exist in metallic carbon nanotubes.