Non-linear intensity dependence of circularly polarized reflectance difference spectra as a probe for spin dynamics in quantum wells

Reflectance difference spectroscopy (RDS)/reflectance anisotropy spectroscopy is traditionally used to study symmetry breaking in cubic crystals using linearly polarized light. In this work, we demonstrate a modified approach using circularly polarized light (RDSc) to investigate spin dynamics in (001)-oriented quantum well structures. While standard RDS generates a homogeneous spin distribution, RDSc creates spin-polarized carriers in the conduction band. We show that the resulting anisotropy line shape remains consistent with standard RDS; however, the signal strength is sensitive to carrier spin relaxation. By analyzing the dependence of the RDSc signal strength on probe light intensity, we successfully monitored the spin dynamics of photogenerated carriers. Our results reveal that the RDSc strength is highly intensity-dependent, establishing the non-linear response of this technique as an effective, non-invasive method for studying spin evolution and relaxation mechanisms in semiconductor heterostructures.