Theory of Transport in Carbon Nanotube Systems

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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 an effective-mass description of electronic states and close relationship with neutrino physics, absence of backward scattering except for scatterers with a potential range smaller than the lattice constant, the presence of a perfectly transmitting channel when several bands coexist at the Fermi level, and its sensitivity to the presence of inelastic scattering limiting the phase coherence length. The transport of a nanotube containing topological defects such as a Stone-Wales defect and five-and seven-membered rings at a junction of nanotubes have also been clarified. The study has been extended toward electronic states of nanotube caps and their topological aspects and interaction effects on the band structure of semiconducting and metallic nanotubes.