Gate-dependent spin-orbit coupling in multi-electron carbon nanotubes

TL;DR

This paper demonstrates the dependence of spin-orbit coupling on electron occupation in multi-electron carbon nanotube quantum dots, revealing a unique curvature-induced effect with potential for spintronics and quantum computing.

Contribution

It shows for the first time that spin-orbit coupling in nanotube quantum dots varies systematically with electron number, including sign changes, due to curvature effects.

Findings

Spin-orbit coupling depends on electron occupation.

Sign change in spin-orbit coupling observed.

Curvature-induced effects explain the coupling behavior.

Abstract

Understanding how the orbital motion of electrons is coupled to the spin degree of freedom in nanoscale systems is central for applications in spin-based electronics and quantum computation. We demonstrate this coupling of spin and orbit in a carbon nanotube quantum dot in the general multi-electron regime in presence of finite disorder. Further, we find a strong systematic dependence of the spin-orbit coupling on the electron occupation of the quantum dot. This dependence, which even includes a sign change is not demonstrated in any other system and follows from the curvature-induced spin-orbit split Dirac-spectrum of the underlying graphene lattice. Our findings unambiguously show that the spin-orbit coupling is a general property of nanotube quantum dots which provide a unique platform for the study of spin-orbit effects and their applications.