Magnetoconductance of carbon nanotubes

As a result of the interaction between the spin and the magnetic field (B), special step structures are predicted to exist in the ballistic magnetoconductance of carbon nanotubes. The electronic structure of a carbon nanotube drastically changes from a metal (semiconductor) to a semiconductor (metal) during the variation of the magnetic flux. When the spin-B interaction is neglected, the Fermi level only touches the conductance and valence bands of a metallic nanotube. This paramagnetic interaction could make the subbands cross and intersect with the Fermi level within a certain magnetic-flux range; the ballistic magnetoconductance thus exhibits step structures. Such special structures are expected to be observable at low temperature (<1 K) and bias voltage (<0.1 mV). Moreover there exists another effect, the doping effect, which could lead to step structures even without the spin-B interaction.