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

J K Furdyna and M Dobrowolska Department of Physics, University of Notre Dame, Notre Dame, IN, USA

Abstract. 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. 1

1. Introduction The spin exchange interaction between carrier spin in two coupled QD structures is an interesting phenomenon to be explored, [1] since it could provide opportunity to manipulate spin state in QD structure. For example, the spin interaction between the carriers in pairs of coupled QDs can be used to polarize the spin state of carriers in the QDs. Experimental observation of such exchange interaction, however, is rather difficult in symmetrically coupled QD system due to indistinguishable PL signal from two QDs. We strategically design asymmetrically coupled QD structure comprised of two QD layers having different band gap energy. In this double layer structure the spin polarization of carriers in one QDs is expected to be affected by the spin of carriers in the other QDs, which are coupled each other. We used polarization selective magneto-optical photoluminescence (PL) measurement to observe magnetic field dependence of polarization, from which we are able to study spin polarization of carriers in QDs and thus the spin-dependent exchange interaction in paired QDs.