Aharonov-Bohm spectral features and coherence lengths in carbon nanotubes

The electronic properties of carbon nanotubes are investigated in the presence of disorder and a magnetic field parallel or perpendicular to the nanotube axis. In the parallel field geometry, the ${\ensuremath{\varphi}}_{0}$-periodic $({\ensuremath{\varphi}}_{0}=hc/e)$ metal-insulator transition induced in metallic or semiconducting nanotubes is shown to be related to a chirality-dependent shifting of the energy of the van Hove singularities (VHS's). The effect of disorder on this magnetic-field-related mechanism is considered with a discussion of mean free paths, localization lengths, and magnetic dephasing rate in the context of recent experiments.