Effects of Magnetic Field on Quantum Phenomena in Carbon Nanotubes

点击翻译按钮获取中文摘要

Graphite needles called carbon nanotubes (CN's) were discovered recently and have been a subject of an extensive study. A CN is a few concentric tubes of two-dimensional (2D) graphite consisting of carbon-atom hexagons arranged in a helical fashion about the axis. The distance of adjacent sheets or walls is larger than the distance between nearest neighbor atoms in a graphite sheet and electronic properties are dominated by those of a single layer CN. The purpose of this project is to study effects of magnetic fields on electronic properties of carbon nanotubes theoretically.Carbon nanotubes can be either a metal or semiconductor, depending on their diameters and helical arrangement. This condition is obtained based on the band structure of a 2D graphite sheet and periodic boundary conditions along the circumference direction. This result was first predicted by means of a tight-binding model ignoring the effect of the tube curvature and can be well reproduced in a κ・ρ method or an effective-mass approximation. In fact, the effective-mass scheme has been used successfully in the study of wide varieties of electronic properties of CN.In this project we have discussed effects of magnetic field on quantum transport of nanotubes based on the κ・ρ method combined with a tight-binding model, such as(1) the calculation of the conductance based on analytic treatment of multiple scattering on lattice vacancies in magnetic fields,(2) the calculation of the conductance of a junction sytem in magnetic fields and the demonstration on its field-independence,(3) the establishment of the long-wavelength phonons in nanotubes and the prediction of a huge positive magnetoresistance at high temperatures, and(4) the calculation of scattering phase shift at caps of nantobues and discrete energy levels of capped nanotubes.