Large spin-orbit coupling in carbon nanotubes

TL;DR

This paper reports a significantly larger spin-orbit coupling in carbon nanotubes than previously observed, with potential implications for spintronic applications, although its origin remains unexplained by current theories.

Contribution

It presents experimental evidence of an order of magnitude increase in spin-orbit coupling in carbon nanotubes, surpassing prior measurements and theoretical expectations.

Findings

Zero-field spin splitting up to 3.4 meV

Effective magnetic field of 29 T along nanotube axis

Large spin-orbit coupling not explained by existing theories

Abstract

It has recently been recognized that the strong spin-orbit interaction present in solids can lead to new phenomena, such as materials with non-trivial topological order. Although the atomic spin-orbit coupling in carbon is weak, the spin-orbit coupling in carbon nanotubes can be significant due to their curved surface. Previous works have reported spin-orbit couplings in reasonable agreement with theory, and this coupling strength has formed the basis of a large number of theoretical proposals. Here we report a spin-orbit coupling in three carbon nanotube devices that is an order of magnitude larger than measured before. We find a zero-field spin splitting of up to 3.4 meV, corresponding to a built-in effective magnetic field of 29 T aligned along the nanotube axis. While the origin of the large spin-orbit coupling is not explained by existing theories, its strength is promising for applications of the spin-orbit interaction in carbon nanotubes devices.