Dynamic polarization of electron spins interacting with nuclei in semiconductor nanostructures

TL;DR

This paper introduces a novel mechanism for electron spin polarization in semiconductor nanostructures, utilizing nuclear spin fluctuations and hyperfine interactions, achieving significant spin polarization without polarized light.

Contribution

It proposes a new spin orientation method driven by nuclear spin fluctuations and demonstrates experimental evidence in quantum dots.

Findings

Electron spin polarization up to 30% observed at 17 mT.

Predicted 100% polarization in ideal conditions with weak magnetic fields.

New mechanism does not require polarized light for spin orientation.

Abstract

We suggest a new spin orientation mechanism for localized electrons: $dynamic~electron~spin~polarization~provided~by~nuclear~spin~fluctuations$. The angular momentum for the electrons is gained from the nuclear spin system via the hyperfine interaction in a weak magnetic field. For this the sample is illuminated by an unpolarized light, which directly polarizes neither the electrons nor the nuclei. We predict, that for the electrons bound in localized excitons 100% spin polarization can be reached in longitudinal magnetic fields of a few millitesla. The proof of principle experiment is performed on momentum-indirect excitons in (In,Al)As/AlAs quantum dots, where in a magnetic field of 17 mT the electron spin polarization of 30% is measured.