Electrically Tunable Spin Polarization in a Carbon-Nanotube Spin Diode

TL;DR

This paper demonstrates a spin diode using a carbon nanotube quantum dot with tunable spin polarization, achieved through electrical control of gate and bias voltages, without the need for high magnetic fields or optical methods.

Contribution

It introduces an electrically tunable spin diode based on a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead, enabling precise control of spin polarization.

Findings

Current is spin-polarized in one bias direction.

Spin polarization can be fully tuned by gate and bias voltages.

The device operates without high magnetic fields or optical methods.

Abstract

We have studied the current through a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead. For the values of gate voltage at which the normal lead is resonant with the single available non-degenerate energy level on the dot, we observe a pronounced decrease in the current for one bias direction. We show that this rectification is spin-dependent, and that it stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. Our results imply that the current is spin-polarized for one direction of the bias, and that the degree of spin polarization is fully and precisely tunable using the gate and bias voltages. As the operation of this spin diode does not require high magnetic fields or optics, it could be used as a building block for electrically controlled spintronic devices.