Interaction-driven giant orbital magnetic moments in carbon nanotubes

TL;DR

This study reveals that electron-electron interactions cause exceptionally large orbital magnetic moments in carbon nanotube quantum dots, challenging existing models and highlighting the importance of many-body effects.

Contribution

It demonstrates that giant orbital magnetic moments in carbon nanotubes arise from electron-electron interactions, requiring self-energy corrections in theoretical models.

Findings

Magnetic moments up to seven times larger than expected

Magnetic moment decreases with added electrons, contradicting shell filling

Giant magnetic moments explained by electron-electron interactions

Abstract

Carbon nanotubes continue to be model systems for studies of confinement and interactions. This is particularly true in the case of so-called "ultra-clean" carbon nanotube devices offering the study of quantum dots with extremely low disorder. The quality of such systems, however, has increasingly revealed glaring discrepancies between experiment and theory. Here we address the outstanding anomaly of exceptionally large orbital magnetic moments in carbon nanotube quantum dots. We perform low temperature magneto-transport measurements of the orbital magnetic moment and find it is up to seven times larger than expected from the conventional semiclassical model. Moreover, the magnitude of the magnetic moment monotonically drops with the addition of each electron to the quantum dot directly contradicting the widely accepted shell filling picture of single-particle levels. We carry out quasiparticle calculations, both from first principles and within the effective-mass approximation, and find the giant magnetic moments can only be captured by considering a self-energy correction to the electronic band structure due to electron-electron interactions.