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Effects of Magnetic Field on Quantum Phenomena in Carbon Nanotubes

磁场对碳纳米管量子现象的影响

基本信息

批准号：
11165211
负责人：
ANDO Tsuneya
金额：
$ 4.93万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas (A)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

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.

被称为碳纳米管（CN）的石墨针最近被发现，并已成为广泛研究的主题。CN是由围绕轴以螺旋方式排列的碳原子六边形组成的二维（2D）石墨的几个同心管。相邻片或壁的距离大于石墨片中最近邻原子之间的距离，并且电子性质由单层CN的电子性质主导。本项目的目的是从理论上研究磁场对碳纳米管电子性质的影响。碳纳米管可以是金属或半导体，这取决于它们的直径和螺旋排列。该条件是基于二维石墨片的能带结构和沿周向沿着的周期性边界条件获得的。这一结果首先是通过紧束缚模型预测的，忽略了管曲率的影响，可以很好地再现在κ·ρ方法或有效质量近似。实际上，有效质量方案已经成功地应用于CN的各种电子性质的研究。本项目基于κ·ρ方法结合紧束缚模型讨论了磁场对纳米管量子输运的影响，如（1）基于磁场中晶格空位多次散射的解析处理计算电导，（2）磁场中结系统电导的计算及其场无关性的证明;（3）纳米管中长波长声子的建立及其高温下巨大的正磁阻效应的预测;（4）纳米管帽散射相移和帽纳米管离散能级的计算。