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

A novel spin orientation mechanism---dynamic electron spin polarization---has been recently suggested in Phys. Rev. Lett. 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.