碳纳米管在轴向磁场中的电子态密度  

The Density of States of Nanotubes in Axial Magnetic Field

作　　者：杨化通[1] 张浩[1] 董锦明[1] 

机构地区：[1]南京大学物理系,固体微结构物理实验室,南京210093

出　　处：《南京大学学报（自然科学版）》2002年第1期36-42,共7页Journal of Nanjing University（Natural Science）

摘　　要：研究了纳米碳管在接近轴向的磁场中的Aharonov Bohm效应 ,计算结果表明纳米碳管的电子态密度会被磁场剧烈地改变 ,所有的纳米碳管都会出现一个随穿过的磁通量周期化的能隙 ,周期为h/e ,因此纳米碳管的导电性也随磁通周期地改变 ;但对不同类型 (金属型和半导体型 )的纳米碳管 。Carbon nanotubes are composed of individual graphene sheets rolled into seamless hollow cylinders with diameters ranging from 1 nm to about 20 nm. The scale of the nanotubes is very small, making them ideally suited for investigation of Arharonov-Bohm interference effects at the single-molecule level caused by magnetic flux passing through the cross section of the nanotubes. Such interference effects have been observed by Bachtold et al. The main purpose of this work is to theoretically investigate the change of the electron density of states of the nanotubes caused by Aharonov-Bohm interference effects. We adopt the tight-binding Hamiltonian which retains only the nearest neighbor π-like hopping matrix elements between |p ⊥> orbitals (one per carbon atom) orientated normal to the tube surface, and use the method of Green's function. It is found that the density of states can be markedly changed by the external magnetic field, and an energy gap emerges whose width oscillates with the flux passing through the cross section of the nanotube. The period of the oscillation is  0=h/e. But for different nanotubes, the patterns of this Arharonov-Bohm oscillation are quite different. For all of metallic nanotubes, which satisfy n 1-n 2=2, k=1,2,3..., there is one oscillating in a period, but for semiconducting nanotubes, with n 1-n 2=2k±1, k=1,2,3..., there are two oscillatings in a period. We also consider the case where the magnetic field is not accurately along the axis of the tube. It is found that in this case the Arhoronov-Bohm oscillation of the energy gap rapidly decays with the magnetic flux. The oscillation amplitude of the energy gap rapidly decreases with the increase of the magnetic flux and the gap will vanish at last.

关 键 词：碳纳米管 AHARONOV-BOHM效应 轴向磁场 电子态密度 

分 类 号：O613.71[理学—无机化学] O488[理学—化学]