Exciton-Mn exchange interactions as a function of translational wavevector in Cd1-xMnxTe quantum wells

The exchange interaction between excitons and manganese ions have been studied in wide quantum wells of Cd 1-x Mn x Te with Cd 1-y Mg y Te barriers. The widths L of the wells are sufficiently large for the excitons to be described by the centre of mass approximation, in which the translational wavevector is quantised according to K z = Nπ/L. Excitonic transitions with different values of the quantisation index N can be resolved in the optical spectra. The giant Zeeman splittings induced by a magnetic field then enable the separate determination of the exchange energy for each value of the wavevector. We find that the quantity N 0 (α - β), which describes the exchange splitting, is constant to within 3% over the range of wavevectors up to 4 × 10 6 cm -1.