Electric and magnetic field effects on electronic structure of straight and toroidal carbon nanotubes

Nanotubes have been proved as promising candidates for many technological applications in the nanoscale
word and different physical properties have been studied and measured along the few recent years. Here we
investigate the role played by external magnetic and electric fields on the electronic properties of toroidal and
cylindrical straight carbon nanotubes. A single-π band tight-binding Hamiltonian is used and two types of
model-calculations are adopted: real-space renormalization techniques, based on Green function formalism,
and straight diagonalization calculation. Both electric and magnetic fields may be properly applied, in different
configurations, to modify the energy spectra and transport properties, providing metal-insulator transitions for
particular tube geometries.