Nanometer-scale loop currents and induced magnetic dipoles in carbon nanotubes with defects

In metallic carbon nanotubes with defects, the electric current flow is expected to have characteristic spatial patterns depending on the nature of the defects. Here, we show, using first-principles transport calculations, that locally rotating loop currents in nanometer scale can be generated near defects in carbon nanotubes by quantum interference of conducting and quasi-bound states of electrons. The loop currents appear at energies near transmission dips, having opposite directions at lower- and higher-energy sides of the transmission dips and disappearing exactly at the centers of the dips. Temporal modulations of gate voltage around a transmission dip can produce oscillating magnetic dipoles, inducing magnetic fields that reflect characteristics of defects. This generation of loop currents and magnetic dipoles by quantum interference can generally occur in any nanostructure and it is potentially useful for novel electronic and magnetic nanodevices.