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

Abstract

We have studied self-assembled QDs in the form of single-and double-QD layer systems. The double layers were formed either from CdSe and CdZnSe layers, or from CdSe and CdZnMnSe layers, separated by ZnSe barriers. When a magnetic field is applied to the CdSe/CdZnSe double-QD layer, the intensities of the circularly polarized PL peaks corresponding to the CdSe and CdZnSe layers exhibit significant differences, reflecting correspondingly large differences in the degrees of spin polarization of the CdSe and the CdZnSe QDs. This contrasts with the PL observed on single-layer CdSe or CdZnSe QD reference structures, both of which show nearly identical dependences on the field. The behavior observed on the double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in the coupled QD pairs. Such spin interaction is even more pronounced in double-layer structures in which CdZnMnSe QW or QDs are used instead of CdZnSe QDs, reflecting the high potential of magnetic quantum structures in the context of spin-polarized applications. IntroductionSpin states in quantum dots (QDs) have recently been proposed as viable candidates for quantum bits in quantum computing.[1] As an important step toward this application one must have a good understanding of spin phenomena in QDs, as well as the ability to control and manipulate spins localized in this way. Coupled QD pairs are especially interesting in this context, since they constitute the simplest and at the same time the most informative QD system for studying spin interactions in a highly-localized geometry. Theoretical calculations [2] predict that when QDs are coupled, spins localized in one QD tend to align anti-parallel (antiferromagnetically) with those in is neighbor. This automatically provides a handle for manipulating spin states in the QD geometry.

Epitaxial GaMnAs layers and nanostructures with anisotropy in structural and magnetic properties

“…Their strain fields, caused by Stranski-Krastanow island formation, may penetrate into the neighboring continuous magnetic layer, possibly also inducing magnetization in growth direction. Furthermore, interaction of carriers in the discrete energy states of the QDs with the magnetic layer can be studied in the III-V material system, as it has been recently demonstrated in the II-VI material system by Lee et al [6].…”

Optical and Structural Properties of Zn–Cd–Mn–Se Double Quantum Well Systems

“…Extensive studies have been made on spin-related exciton states, such as electronhole exchange interaction, [1][2][3] g-factor, 4,5) energy levels in magnetic field, 6) spin-polarized exciton injection, 7) spin dynamics and relaxation, 8,9) and inter-dot exchange interaction. 10,11) We reported tunneling transfer of spin-polarized excitons in coupled diluted magnetic semiconductor (DMS) and non-DMS (NMS) double quantum well (DQW). 12,13) In this paper, we describe on the optical and structural properties of DQW consisting of ZnCdSe and ZnCdMnSe wells separated by a ZnSe barrier.…”

Formation and optical properties of stacked CdSe self-assembled quantum dots on ZnxCdyMg1−x−ySe barriers

“…One reason for this recent interest is due to the fact that they can be regarded as ideal solid state "artificial atoms" in which excitons are confined in quasizero dimensions so the physical phenomena ͑Stark effect, 5 Zeeman effect, 6 Overhauser effect, 7 spin polarization effects, 8,9 and others͒ that exhibit are often related more to the atomic physics rather than to the semiconductor bulk physics. One reason for this recent interest is due to the fact that they can be regarded as ideal solid state "artificial atoms" in which excitons are confined in quasizero dimensions so the physical phenomena ͑Stark effect, 5 Zeeman effect, 6 Overhauser effect, 7 spin polarization effects, 8,9 and others͒ that exhibit are often related more to the atomic physics rather than to the semiconductor bulk physics.…”