Experimental evidence for antiferromagnetic spin–spin interaction between carriers localized in coupled quantum dots

A self-assembled quantum dot (QD) system consisting of adjacent CdSe and CdZnMnSe QD layers in a ZnSe matrix was investigated using polarization-selective magnetophotoluminescence (PL). We can unambiguously identify which QD peak originates from which material, because PL from CdZnMnSe (a diluted magnetic semiconductor) exhibits a large Zeeman shift in the presence of a magnetic field. Significant enhancement of the degree of σ− circular polarization emitted by the nonmagnetic CdSe QDs is observed in the double layer system, as compared to that observed in similar CdSe QDs without the influence of neighboring CdZnMnSe QDs. This behavior can be understood in terms of antiferromagnetic interaction between carrier spins localized in pairs of CdSe and CdZnMnSe QDs that are electronically coupled.