Orbital magnetic moments in pure and doped carbon nanotubes

Abstract

The unusual band structure of carbon nanotubes (CNs) results in their remarkable magnetic properties. The application of magnetic field 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 $\mu_{orb}$ in the nanotube. These moments are studied both in pure and hole- or electron-doped CNs, isolated or in a circuit. Remarkably, $\mu_{orb}$ in pure CNs depends uniquely on their original conducting properties, length, and temperature, but it does 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 full electron-hole symmetry in doped tubes is also revealed.Comment: 10 pages, 11 figures, submitted to Phys. Rev.