Dynamic polarization of electron spins in indirect band gap (In,Al)As/AlAs quantum dots in weak magnetic field: experiment and theory

TL;DR

This paper investigates a newly discovered dynamic electron spin polarization mechanism in (In,Al)As/AlAs quantum dots, demonstrating how its sign varies with magnetic field parameters through combined experimental and theoretical analysis.

Contribution

It provides the first comprehensive experimental and theoretical study of the sign-changing dynamic electron spin polarization in indirect band-gap quantum dots under weak magnetic fields.

Findings

Spin polarization sign changes over time and magnetic field parameters.

Experimental and theoretical results are in good agreement.

The mechanism operates under unpolarized optical excitation in weak magnetic fields.

Abstract

A novel spin orientation mechanism - dynamic electron spin polarization has been recently suggested in Phys. Rev. Lett. $\mathbf{125}$, 156801 (2020). It takes place for unpolarized optical excitation in weak magnetic fields of the order of a few millitesla. In this paper we demonstrate experimentally and theoretically that the dynamic electron spin polarization degree changes sign as a function of time, strength of the applied magnetic field and its direction. The studies are performed on indirect band-gap (In,Al)As/AlAs quantum dots and their results are explained in the framework of a theoretical model developed for our experimental setting.