Asymmetric double quantum wells as exciton spin separator

Exciton recombination in asymmetric CdMgTe/CdTe/CdMgTe/CdTe/CdMnTe double quantum wells (ADQW) with different barrier widths is studied in magnetic field up to 10T. As grown structures were subjected to temperature annealing to introduce Mn and Mg atoms from the barriers into the CdTe quantum wells (QW). At low fields exciton transition in QW with magnetic impurity (Mn) is higher in energy than that in QW with nonmagnetic impurity (Mg), and interwell exciton relaxation is fast independently on the spin state. In contrast, at high fields, when the energy order reverses, an unexpectedly low relaxation rate of sigma(-) polarized excitons from nonmagnetic QW to the ground sigma(+) polarized state in magnetic QW has been observed. Effect strongly correlates with hh-lh splitting value Delta(hh-lh) and discussed in terms of valence band mixing. Such a slowing down of relaxation allows separation of oppositely polarized excitons in different QWs.