Abstract
Self-assembled $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots (QDs) are studied by means of circular polarization-resolved photoluminescence and pump-probe differential reflectivity as a function of the excitation density using a linear polarized pump laser. We observe an unexpected large circular polarization anisotropy, which decreases with increasing excitation density for both experimental techniques. Comparison of the respective polarization degrees reveals a ratio of approximately 0.2. Moreover, the reflection measurements reveal circular dichroism with a ratio of ${\ensuremath{\Theta}}^{+}∕{\ensuremath{\Theta}}^{\ensuremath{-}}=1.16$. Circular dichroism in semiconductor QDs can be explained by the induced magnetism as a result of light confinement in QDs, providing an anisotropic coupling between the pump-induced QD exciton and the circularly polarized probe field.
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