Determination of excitonic parameters of the A polariton of CdS from magnetoreflectance spectroscopy

The magnetoreflectance of the A exciton of CdS is studied for fields up to 10 tesla for the orientations →H⊥→c and (→H, →c)=45^∘. A quantitative line-shape analysis is made of the spectra using the model of polaritons with spatial dispersion and Pekar's abc and, considering damping and exciton-free surface layer it shows a remarkable good agreement between experiments and calculations. This allows a very distinct investigation of the splitting parameters of the exciton and the corresponding bands. The g values are measured to be g_e⊥=g_e∥=1.75±0.05 and g_A∥=1.25±0.1. The longitudinal-transverse H(ΔLT) and, for the first time, the singlet-triplet splitting (Δ₅₆), both resulting from exchange interaction, are determined to ΔLT=(2.1±0.03) meV and Δ₅₆=(0.2±0.03) meV.