Spin relaxation of excitons in nonmagnetic quantum dots: Effect of spin coupling to magnetic semiconductor quantum dots

Abstract

The effect of spin coupling on the spin polarization of exciton was investigated in double quantum dot (QD) structures, one layer consisting of self-assembled nonmagnetic CdZnSe quantum QDs, and the other of CdMnSe diluted magnetic semiconductor QDs, both layers embedded in ZnSe. The magneto-photoluminescence (PL) studies on this double-layer structure were carried by detecting a single circular polarization in order to investigate the polarization dependence of the PL intensity. We have observed two well separated PL peaks in double QDs, corresponding to emissions from the CdZnSe and CdMnSe QD layers, respectively. It appears that the degree of the PL polarization emitted by the CdZnSe QDs in this double-layer structure is much larger than that observed in a single layer of nonmagnetic CdZnSe QDs. We discussed this enhancement of polarization in terms of antiparallel spin interaction between excitons localized in the nonmagnetic QDs and in the magnetic QDs.

Antiferromagnetic interaction in coupled CdSe/ZnMnSe quantum dot structures

“…Such dependence on the spacer thickness is somewhat expected, as common magnetic interactions such as magnetic dipolar coupling and exchange interaction are known to be a sensitive function of the separation between two coupled magnetic layers. 22 Together with the results from earlier reports, 17,18 the observed AFC seems to be effective when the spacer thickness is in the range of 5-40 nm.…”

“…Instead, it should arise from an anti-parallel spin interaction between the CdSe QDs and the DMS. Anti-parallel interaction has been reported earlier in a number of coupled quantum layer structures, [15][16][17][18][19] which was suggested to originate from AFC of photo-generated carriers/excitons spins between the QDs and DMS. Up to now, a direct proof for the suggested model is still lacking.…”

Power and temperature dependent magneto-photoluminescence of the asymmetric double layers of quantumdots

“…The conduction and the valence bands of the semiconductor undergo the Zeeman splitting when a field is applied, and thus photo-excited carriers prefer to relax to the lowest spin sublevels before recombination. In the polarization selective optical measurements, since the transitions between the spin-up (spin-down) states of the conduction and the valence bands correspond to the s À (s + ) polarization, the PL intensity of each polarization indicates directly the number of spin-polarized carriers in the QD system [11].…”

Growth and magneto-optical properties of CdSe/ZnMnSe self-assembled quantum dots

“…For example, the effect of three-dimensional confinements on the magnetic polaron and magnetic fluctuation in nanoscale were studied by magneto-optical spectroscopy based on DMS QD systems [4][5][6]. Furthermore, the anti-parallel spin interaction between carriers localized in the zero-dimensional structure was identified in coupled QD systems consists of DMS and non-DMS materials [7,8]. In spite of such a great deal of attention given to understand new physical properties arising from incorporation of magnetic ions in the QD systems, the detail growth process for QD formation and the evolution of dots in DMS QD systems have not been systematically studied.…”