Polarization selective magneto-optical study on the coupled quantum dots using resonant excitation

We have studied a double-layer self-assembled quantum dot (QD) structures consisting of non-magnetic CdSe and magnetic CdMnSe. Transmission electron microscopy image shows that QDs are formed within the CdSe and CdMnSe layers, and they are vertically correlated in the system. The strong interband ground state transition was observed in magneto-photoluminescence (PL) experiments. In contrast to a typical behavior for many low-dimensional systems involving diluted magnetic semiconductors (DMSs), where PL signal dramatically increases when an external magnetic field is applied, we have observed a significant decrease of the PL intensity as a function of magnetic field in the double-layer structures where the alternating QD layers contain the DMS and non-DMS QDs. We attribute such effect to carrier transfer from non-magnetic CdSe dots to magnetic CdMnSe dots due to the large Zeeman shift of the band edges of DMS QDs in magnetic field. Since the band alignment of QD structure strongly depends on the spin states of system, we performed polarization-selective PL measurement to identify spin-dependent carrier tunneling in this coupled system.