Measuring electron orbital magnetic moments in carbon nanotubes

TL;DR

This paper experimentally measures and confirms the large orbital magnetic moments of electrons in individual carbon nanotubes, elucidating their role in magnetic properties and electronic structure.

Contribution

First direct electrical measurements of orbital magnetic moments in individual carbon nanotubes, confirming theoretical predictions.

Findings

Orbital magnetic moments are much larger than the Bohr magneton.

Energy shifts in electronic states due to magnetic field are observed.

Results match predicted values for orbital magnetic moments.

Abstract

The remarkable transport properties of carbon nanotubes (NTs) are determined by their unique electronic structure (1). The electronic states of a NT form one-dimensional electron and hole subbands which, in general, are separated by an energy gap (2,3). States near the energy gap are predicted to have a large orbital magnetic moment much larger than the Bohr magneton (4,5). The moment is due to electron motion around the NT circumference. This orbital magnetic moment is thought to play a role in the magnetic susceptibility of NTs (6-9) and the magneto-resistance observed in large multi-walled NTs (10-12). However, the coupling between magnetic field and the electronic states of an individual NT has not been experimentally quantified. We have made electrical measurements of relatively small diameter (2 - 5 nm) individual NTs in the presence of an axial magnetic field. We observe energy shifts of electronic states and the associated changes in subband structure. Our results quantitatively confirm predicted values for orbital magnetic moments in NTs.