Optical spin polarization by coherent magnetoabsorption generation

The spin orientation of optical emissions in GaAs_1-xSb_x/GaAs quantum wells (QWs) is investigated through magneto-photoluminescence measurements. Notably, spin-dependent intensity oscillations emerge in high magnetic fields, originating from interband transitions between Landau levels in the GaAs barriers and described by the magnetoabsorption effect. These spin-resolved absorption resonances, when coupled with coherent relaxation toward the ground-state optical transition in the type-II QWs lead to pronounced spin polarization peaks. A theoretical framework based on rate equations for spin-split states demonstrates that such polarization is only achieved when spin-flip times are comparable to or exceed the optical recombination time, ensuring that spin orientation is maintained from carrier excitation to optical recombination. This prediction is experimentally validated though time-resolved measurements with circularly polarized excitation, where a spin lifetime of 3.5 ns is determined, confirming the role of magnetoabsorption in sustaining spin coherence.