Spin relaxation of excitons in nonmagnetic quantum dots: Effect of spin coupling to magnetic semiconductor quantum dots

The effect of spin coupling on the spin polarization of exciton was investigated in double quantum dot (QD) structures, one layer consisting of self-assembled nonmagnetic CdZnSe quantum QDs, and the other of CdMnSe diluted magnetic semiconductor QDs, both layers embedded in ZnSe. The magneto-photoluminescence (PL) studies on this double-layer structure were carried by detecting a single circular polarization in order to investigate the polarization dependence of the PL intensity. We have observed two well separated PL peaks in double QDs, corresponding to emissions from the CdZnSe and CdMnSe QD layers, respectively. It appears that the degree of the PL polarization emitted by the CdZnSe QDs in this double-layer structure is much larger than that observed in a single layer of nonmagnetic CdZnSe QDs. We discussed this enhancement of polarization in terms of antiparallel spin interaction between excitons localized in the nonmagnetic QDs and in the magnetic QDs. (C) 2006 American Institute of Physics.