Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field

TL;DR

This paper demonstrates electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field, achieving circularly polarized light emission and nuclear spin polarization control without external magnetic fields.

Contribution

It introduces a method for electrically injecting spin-polarized electrons into a quantum dot, enabling nuclear spin polarization control at zero magnetic field.

Findings

Achieved up to 35% circular polarization in electroluminescence at zero magnetic field.

Observed Overhauser shift indicating dynamic nuclear polarization.

Demonstrated electrical control of nuclear spins in a quantum dot.

Abstract

The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region. We measure an Overhauser shift of several $\mu$eV at zero magnetic field for the positively charged exciton (trion X$^+$) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. This study paves the way for electrical control of nuclear spin polarization in a single quantum dot without any external magnetic field.