Dynamical Processes of Electron-Spin Systems Photo-Excited in Semiconductor Quantum Dots

本计画的目的是（1）了解非磁性与磁性半导体中量子限制激子的单重态-三重态自旋转换与限制激子磁极化子的弛豫动力学;（2）探讨限制激子-自旋复合系统所固有的新现象。材料为CuCl半导体量子点和CdMnTe半磁性半导体混晶。在后一种系统中，激子被限制在合金势威尔斯中，即自然生长的量子点中。CuCl量子点中的受限激子：（1）在4K磁致发光光谱中，发现在法拉第和Voigt几何构型下，局域激子发光的强度增强和光谱修正都发生在CuCl量子点中。这些结果清楚地表明，由于激子限制，部分地允许到/从自旋三重态（暗激子态）的光学跃迁，并且在纵向和纵向之间发生混合。 ...更多信息 横向激子(2)通过双光子共振激发到双激子态，发现了对应于双激子自旋三重态的稳定J=2态。此外，J=0的双激子显示出非常有效的激光，这来自于双激子的超辐射性质。(3)磁致发光和吸收的时间行为和温度依赖性的测量可以阐明自旋三重态激子在其平移运动中的作用和动力学. CdMnTe中的局域束缚激子：（1）在合金势威尔斯中局域束缚激子的强烈选择性激发下，发现了一个新的非线性发光带，该带具有巨磁光效应和超快衰减。这种发光及其自旋记忆性可能与定域激子磁极化子的多体效应有关。(2)通过瞬态吸收的测量及其对磁场的依赖性，阐明关联电子-自旋系统的超快弛豫过程是十分必要的。少

The purpose of this project is (1) to know the singlet-triplet spin conversion of quantum-confined excitons and the relaxation dynamics of confined exciton magnetic polarons in non-magnetic and magnetic semiconductors and (2) also to approach to new kinds of phenomena inherent to confined exciton-spin complex systems. The materials are CuCl semiconductor quantum dots and mixed crystals of CdMnTe semi-magnetic semiconductor. In the latter system, excions are confined in alloy potential wells, that is, naturally grown quantum dots.1. Confined excitons inCuCl quantum dots : (1) In the magneto-luminescence spectra at 4K, it has been found that the intensity enhancement and the spectral modification of the localized exciton luminescence occur both under Faraday and Voigt geometries. These results clearly show that, due to the exciton confinement, the optical transition to/from the spin-triplet state (dark exciton state) is partially allowed and the mixing occurs between the longitudinal and … More transverse excitons. (2) By means of two-photon resonance excitation into biexciton states, there has been found the stable J=2 state which corresponds to the spin-triplet state of biexciton. Furthermore, the J=0 biexciton shows very efficient lasing which comes from the superradiant nature of the biexciton. (3) The measurement of temporal behavior and temperature dependence of the magneto-luminescence and absorption may clarify the role and the dynamics of spin-triplet excitons confined in their translational motion.2. Locally confined excitons in CdMnTe : (1) Under the intense, selective excitation of locally confined excitons in alloy potential wells, there has been found a new nonlinear luminescence band which shows giant magneto-optical effects and ultra-fast decay. The luminescence and their spin memory may be related with a certain many-body effect of localized exciton magnetic polarons. (2) It is necessary to clarify the ultra-fast relaxation processes of the correlated electron-spin systems through the measurement of transient absorption and their magnetic field dependence. Less