Magneto‐Reflectance of the B‐Exciton of CdS

The magneto‐reflectance of the B‐exciton of CdS is studied for fields up to 9.0 T. The spectra show a strong anisotropy of the Zeeman‐effect for H ⟂ c; the splitting is proportional to the sum of the g‐values of the valence and the conduction band for H parallel to the wave vector of incident light, but it is proportional to the difference of g‐values for H perpendicular to the wave vector. For the first time a change of the spectra with magnetic field inversion (pole‐changing effect) is observed; it appears for oblique incidence of light and results from the k‐linear term of the valence band. The spectra are discussed by lineshape analysis along the lines of excitonic polaritons. From the excellent agreement between experiments and calculations some new parameters of the B‐exciton can be determined: the g‐value of the B‐valence band g = 0.8 ± 0.1, the diamagnetic shift δdia = (2.0 ± 0.3) μe V/T2, and the different parts of the exchange interaction energy ΔLT = (1.4 ± 0.03) meV, Δ25 = (0.1 ± 0.05) meV and Δ21 = (0.15 ± 0.05) meV.