Exciton magnetic polaron in semimagnetic semiconductor nanocrystals
Exciton magnetic polaron in semimagnetic semiconductor nanocrystals
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DOI：
10.1103/physrevb.55.10613
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发表时间：
1997-04-15
影响因子：
3.7
通讯作者：
laGuillaume, CBA
中科院分区：
文献类型：
--
作者：
Bhattacharjee, AK;laGuillaume, CBA
对稀磁半导体量子点中与电子空穴对相关联的磁极化子进行了理论研究。它是基于有效质量近似的强约束制度，其中包括轻和重空穴带之间的耦合。磁极化子，所产生的sp-d之间的交换相互作用的限制的载流子和磁性离子，被处理在一个自洽的平均场的方法，导致耦合的非线性薛定谔方程的电子和空穴：的本地响应的有效场建模的实验高场磁化曲线在散装。考虑了电子-空穴库仑相互作用。三个耦合方程的精确数值解被用来计算平衡极化子的大小，结合能（E-p），和自旋（S-p）。结果首先呈现为Cd 1-xMnxTe纳米晶体与x = 0.11。随着量子点半径（a）的增大，E-p减小，轨道收缩增大。在小点中，在核心区域接近饱和，E-p随着温度（T）的升高而缓慢降低。在大的点中，E-p（T）朝着波动区域迅速减小，其中E-p与α（-3）成比例。一个类似的温度依赖性得到S-p的波动制度的值，但是，大小无关。由于极化子的形成，光诱导的磁化强度增强被认为是和一个最佳的量子点半径被预测为类似于30埃。我们还计算了E-p作为外加磁场的函数，它显示出依赖于a和T的减小行为。Cd 1-xMnxSe纳米晶体的理论结果与最近报道的光致发光斯托克斯位移随磁场的实验数据显示出良好的一致性。
We present a theoretical study of the magnetic polaron associated with an electron-hole pair in a diluted magnetic semiconductor quantum dot. It is based on the effective-mass approximation in the strong confinement regime, which incorporates the coupling between the light- and heavy-hole bands. The magnetic polaron, arising from the sp-d exchange interaction between the confined carriers and the magnetic ions, is treated in a self-consistent mean-field approach that leads to coupled nonlinear Schrodinger equations for the electron and the hole: The local response to the effective field is modeled by the experimental high-field magnetization curve in the bulk. The electron-hole Coulomb interaction is taken into account. An exact numerical solution of the three coupled equations is used to calculate the equilibrium polaron size, binding energy (E-p), and spin (S-p). Results are first presented for Cd1-xMnxTe nanocrystals with x = 0.11. E-p decreases and the orbital contraction increases with an increasing quantum dot radius (a). In small dots, approaching saturation in the core region, E-p decreases slowly as the temperature (T) increases. In large dots E-p(T) decreases rapidly towards the fluctuation regime, where E-p proportional to a(-3). A similar temperature dependence is obtained for S-p; the fluctuation-regime value is, however, size independent. The light-induced magnetization enhancement due to polaron formation is considered and an optimal quantum dot radius is predicted to be similar to 30 Angstrom. We have also calculated E-p as a function of an applied magnetic field, which shows a decreasing behavior that depends on a and T. Theoretical results for Cd1-xMnxSe nanocrystals show a good agreement with recently reported experimental data on the photoluminescence Stokes shift versus magnetic field.