Orbital magnetic moments in pure and doped carbon nanotubes

The unusual band structure of carbon nanotubes CNs results in their remarkable magnetic properties. The application of magnetic field B parallel to the tube axis can change the conducting properties of the CN from metallic to semiconducting and vice versa. Apart from that, B induces via the Bohm-Aharonov effect orbital magnetic moments orb in the nanotube. These moments are studied both in pure and hole- or electron-doped CNs, isolated or in a circuit. Remarkably, orb in pure CNs depend uniquely on their original conducting properties, length, and temperature but do not depend on the nanotube radius or the particular chirality. In doped nanotubes the magnetic moments can be strongly altered and depend on the radius and chirality. Temperature can even change their character from diamagnetic at low T to paramagnetic at high T. A general electron-hole asymmetry increasing with the doping is found.