Inversion of the spin polarization of localized electrons driven by dark excitons

TL;DR

This paper demonstrates that dark excitons can invert the spin polarization of localized electrons at high excitation densities, revealing a new mechanism influencing spin dynamics in semiconductors.

Contribution

It introduces the novel finding that dark excitons cause an inversion of electron spin polarization at high excitation densities.

Findings

Spin polarization sign reverses at high excitation density.

Dark excitons significantly influence electron spin polarization.

Inversion explained by dark exciton contributions.

Abstract

The creation of free excitons by absorption of circularly polarized photons, and their subsequent fast capture by donors, is at the origin of the spin polarization of donor-bound electrons. The sign of the electronic spin polarization at low density of excitation is, as expected, fixed by the helicity of the exciting light; but at high density of excitation we show that the spin polarization is of the opposite sign. This striking inversion is explained, here, by the contribution of dark excitons to mechanisms of spin polarization of localized electrons.