Defects and external field effects on the electronic properties of a carbon nanotube torus

Abstract

Electronic properties of toroidal carbon nanotubes are studied adopting a single \ensuremath{\pi}-band tight binding Hamiltonian and following real-space renormalization techniques within the Green function formalism. The analysis is restricted to the achiral torus and the dependence of the toroidal energy spectra on its radius and thickness (tube radius) is inferred from the local density of states. The possibility of a metal-insulating transition occurrence in infinite single tubes and toroidal is investigated as functions of magnetic and electric fields applied in distinct configurations. As expected, periodical Aharonov-Bohm oscillations in the local density of states at the Fermi level of the nanostructures are found as a result of the annular symmetry. When substitutional impurities are taken into account such an oscillatory behavior is found to be preserved. Effects of vacancy defects on the electronic properties are also discussed.