Spin splitting in a polarized quasi-two-dimensional exciton gas

TL;DR

This study demonstrates significant spin splitting in a polarized quasi-two-dimensional exciton gas within GaAs/AlAs quantum wells, driven by exciton-exciton interactions without external magnetic fields, with implications for spintronic applications.

Contribution

It provides experimental evidence of large spin splitting caused by exciton interactions in quantum wells, supported by a theoretical model explaining the phenomenon.

Findings

Spin splitting can reach up to 50% of the exciton binding energy.

Splitting increases with excitonic density and decreases over time.

The observed effects are explained by intra-excitonic exchange and exciton-exciton interactions.

Abstract

We have observed a large spin splitting between "spin" $+1$ and $-1$ heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs quantum wells in the absence of any external magnetic field. Time-resolved photoluminescence spectroscopy, under excitation with circularly polarized light, reveals that, for high excitonic density and short times after the pulsed excitation, the emission from majority excitons lies above that of minority ones. The amount of the splitting, which can be as large as 50% of the binding energy, increases with excitonic density and presents a time evolution closely connected with the degree of polarization of the luminescence. Our results are interpreted on the light of a recently developed model, which shows that, while intra-excitonic exchange interaction is responsible for the spin relaxation processes, exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors.