Electronic Structures And Related Properties Of Carbon Nanotubes

In this work the electronic structures of single-walled carbon nanotubes are studied theoretically. Some related experimental phenomena that had not been explained unambiguously are clarified here. And theoretical validity in designing novel quantum devices based on carbon nanotubes is supplied.Firstly, the influence of point defects on the density of states and conductance for metallic carbon nanotubes is studied based on the tight-binding model. Through Green's function method, we find that a virtual bound state is induced by a point defect. From an analytic treatment, the state is determined by the nanotube diameter rather than chirality. The corresponding image of local density of states in real space shows a highly localized state around the defect. At the same time, Friedel Oscillation aroused by defects is found to relate to the nanotube chirality. What is more, a transfer-matrix method is applied to calculate the conductance of defective nanotubes. It is found that the conducting electrons are strongly reflected around the energy of virtual bound states. In addition, the method is applied to discuss the situation of two defects in carbon nanotubes.Secondly, density of states for metallic carbon nanotubes with a magnetic impurity is studied based on a single orbital Anderson model. A rapidly convergent perturbation method for dilute magnetic alloy is employed which divides the Anderson Hamiltonian into two parts, the unperturbed mean field part and the many-particle part. The effect of the mean field part is similar to that of non-magnetic impurities while the many-particle effect decreases rapidly as temperature increases. From an analytic treatment, connection between the Kondo resonance induced by the magnetic impurity and the nanotube parameter is discussed. Density of states for finite-length nanotubes with a magnetic impurity is studied as well. It is found that the Kondo resonance is strongly affected when the level spacing in the finite-length sample becomes larger than the Kondo temperature, in a way that depends on the chirality and the number of unit cells of carbon nanotubes. In addition, the combined effect of a magnetic impurity and a non-magnetic one is analyzed.