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Coupled II-VI semiconductor quantum dots: manipulation of spin polarization by inter-dot exchange interaction

Jacek K. Furdyna 2M. Dobrowolska 2S. Lee 1

1. Korea University, Physics Department, Seoul 136-701, Korea, South
2. University of Notre Dame, Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556, United States


Prospects of employing spin states in quantum dots (QDs) for device applications (e.g., as quantum bits in quantum computing) naturally hinge on the ability to manipulate these states. We will show that exchange interaction makes it possible to change the spin polarization of carriers in one QD by controlling the spin states in an adjacent QD, thus providing a handle for such spin manipulation. We studied self-assembled QDs in the form of double-QD layer systems. For observing interlayer exchange processes, we strategically designed coupled asymmetric structures comprised of QD layers with different QD bandgap energies. The double layers were formed either from CdSe and CdZnSe QDs or from CdSe and CdZnMnSe QDs, separated by ZnSe barriers. We observe well-resolved photoluminescence (PL) peaks originating from the two QD layers, enabling us to identify PL emissions from each QD family, and thus to study the influence of one QD layer on the other. To investigate the spin polarization of carriers in the QDs, we performed polarization-selective magneto-PL experiments by exciting the above structures with unpolarized light, and detecting the PL with the circular polarizations of opposite helicity. When a magnetic field was applied to the CdSe/CdZnSe double-QD layer, intensities of the circularly polarized PL peaks from the CdSe and CdZnSe layers exhibited significant differences, reflecting differences in the degrees of spin polarization of the CdSe and the CdZnSe QDs. This contrasts with single-layer CdSe or CdZnSe QD reference structures, which show nearly identical dependences on the field. The behavior observed on double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in pairs of electronically coupled QDs. Such spin interaction is even more pronounced in double-layer QD structures where CdZnSe QDs are replaced by magnetic CdZnMnSe QDs.


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Presentation: invited oral at E-MRS Fall Meeting 2004, Symposium F, by Jacek K. Furdyna
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-06-29 21:17
Revised:   2009-06-08 12:55