Exotic optical and transport properties of carbon nanotubes

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A carbon nanotube is composed of concentric tubes of rolled two-dimensional graphite sheets, on which hexagons are arranged in a helical fashion about the axis. The diameter of a multi-wall nanotube ranges from 2 to 30 nm and that of a single-wall nanotube lies between 0.7 and 1.6 nm. The maximum length of nanotubes exceeds 1 um. Since the first discovery quite a number of studies have been reported on their electronic properties because of their unique topological structures. The purpose of this project is to study quantum transport in carbon nanotubes and their composite systems with special emphasis on topology of nanotubes.The subjects include the presence of special time reversal symmetry leading to the symplectic universality responsible to the absence of backscattering and the presence of a perfectly conducting channel, effects of various perturbations destroying the symmetry, and the singular dynamical conductivity associated with the perfect channel. Effects of electron-electron interaction on the band structure, strong exciton effects in optical properties, the fine structure of excitons (dark and bright) due to short-range Coulomb interaction and exchange effect and its change in Aharonov-Bohm magnetic flux, and exciton peaks for light polarized perpendicular to the axis were also studied. Further, the absence of inter-wall interaction in usual incommensurate multi-wall nanotubes and effects of electron-phonon interactions on optical phonons and their behavior in the Aharonov-Bohm flux were clarified.