Theory of Transport in Carbon Nanotube Systems

碳纳米管是由轧制的二维石墨片组成的同心管，其上的六边形绕轴螺旋排列。多壁纳米管的直径在2~30 nm之间，单壁纳米管的直径在0.7~1.6 nm之间。纳米管的最大长度超过1微米。自从第一次发现以来，由于它们独特的拓扑结构，人们对它们的电子性质进行了大量的研究。本项目的目的是研究碳纳米管及其复合体系中的量子输运，重点研究纳米管的拓扑结构，包括电子态的有效质量描述和与中微子物理的密切关系，除了势能范围小于晶格常数的散射体外没有后向散射，费米能级上几个能带共存时理想传输通道的存在，以及它对非弹性散射限制相位相干长度的敏感性。含有拓扑缺陷的纳米管，如Stone-Wales缺陷和五元环和七元环在纳米管结合处的传输也得到了澄清。这方面的研究已经扩展到纳米管帽的电子态以及它们的拓扑结构和相互作用对半导体和金属纳米管能带结构的影响。

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.