Optical spin polarization by coherent magnetoabsorption generation

Abstract

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.