Interwell exciton relaxation in semimagnetic asymmetric double quantum wells

Possibility of a magnetic field control of spectral and polarization characteristics of exciton recombination is examined in Cd(Mg,Mn)Te-based asymmetric double quantum wells. At low fields, exciton transition in semimagnetic well is higher in energy than that in nonmagnetic well and interwell exciton relaxation is fast. In contrast, when the energy order of the exciton transitions reverses at high fields, unexpectedly slow relaxation of $\sigma^-$-polarized excitons from nonmagnetic well to the $\sigma^+$-polarized ground state in the semimagnetic well is observed. Strong dependence of the total circular polarization degree on the heavy-light hole splitting $\Delta_{hh-lh}$ in the nonmagnetic well is found and attributed to the spin dependent interwell tunneling controlled by exciton spin relaxation. Such a slowing down of relaxation allows separation of oppositely spin-polarized excitons in adjacent wells.