Spin-detection in a quantum electromechanical shuttle system

TL;DR

This paper models a quantum shuttle system to show how tiny forces, including spin states of endohedral electrons, can be detected through highly sensitive current measurements, advancing molecular force and spin detection techniques.

Contribution

It develops a quantum master equation for a molecular shuttle system that links small forces and spin states to measurable electrical currents, enabling new detection methods.

Findings

Current is highly sensitive to small forces due to exponential tunneling dependence.

Spin states of endohedral electrons can be distinguished via current signals within tens of nanoseconds.

The model predicts potential for detecting static forces and spin states in paramagnetic molecules.

Abstract

We study the electrical transport of a harmonically-bound, single-molecule endohedral fullerene shuttle operating in the Coulomb blockade regime, i.e. single electron shuttling. In particular we examine the dependance of the tunnel current on an ultra-small stationary force exerted on the shuttle. We derive a quantum master equation for the full shuttle system which includes the metallic contacts, the spatially dependent tunnel couplings to the shuttle, the electronic and motional degrees of freedom of the shuttle itself and a coupling of the shuttle's motion to a phonon bath. We analyse the resulting quantum master equation and find that, due to the exponential dependance of the tunnel probability on the shuttle-contact separation, the current is highly sensitive to very small forces. In particular we predict that the spin state of the endohedral electrons of the endohedral fullerene in a large magnetic gradient field can be distinguished from the resulting current signals within a few tens of nanoseconds. This effect could prove useful for the detection of the endohedral spin-state of individual paramagnetic molecules such as N@C60 and P@C60, or the detection of very small static forces acting on a molecular shuttle.