Anti-parallel spin interaction between the carriers in coupled quantum dots

We have performed magneto-photoluminescence (PL) experiments on a self-assembled coupled double quantum dot (QD) system consisting of adjacent CdSe and CdZnSe QD layers. We have observed well separated two PL peaks in such a double layer QD system, corresponding to the CdSe and the CdZnSe QDs. The excitation power dependence of relative PL intensity of the two QD structures clearly shows characteristics of coupled system. This system also exhibits significantly different degree of polarization between CdSe and CdZnSe QD when a magnetic field applied, in contrast to the behavior shown by single-layer CdSe or CdZnSe QD systems, which show nearly identical polarization dependence on the field. The observed behavior was interpreted in terms anti-parallel spin interaction between carriers localized in pairs of QDs that are electronically coupled.