发表机构
Ioffe Institute, Russian Academy of Sciences; Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences（俄罗斯科学院约费研究所; 俄罗斯科学院西伯利亚分院拉扎诺夫半导体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用偏振选择光致发光光谱结合磁场，探究I型(In,Al)As/AlAs量子点中间接带隙激子的级联自旋动力学，推导模型并量化各向异性交换劈裂，揭示零磁场光取向的成因。
AI 中文摘要
我们研究了定域在具有动量空间间接能带结构的I型(In,Al)As/AlAs量子点中激子的自旋动力学。采用了在法拉第几何结构下施加最高5T磁场的偏振选择光致发光光谱，即荧光线窄化技术。实验揭示了间接带隙量子点中激子的级联自旋演化过程：首先是与具有大振子强度的直接激子激发态相关的短期自旋动力学，随后电子弛豫进入布里渊区的X谷，进而发生间接激子的长期自旋动力学。这种两步机制在光致发光的磁场依赖关系中表现出不同特征：光取向的双分量恢复、线偏振向圆偏振的双分量转换以及线偏振平面旋转的存在。与此同时，光取向的抑制呈现出由间接激子态自旋动力学决定的单分量行为。我们在赝自旋形式框架内推导了解析表达式，定量描述了观测到的依赖关系，并给出各向异性交换劈裂的估计值：直接激子为210μeV，间接激子为1.3μeV。采用密度矩阵形式框架的进一步分析与赝自旋模型计算结果吻合良好，表明零磁场下有限的光取向源于间接激子态的各向异性劈裂与X谷电子态因与核的超精细相互作用产生的劈裂大小相当。
英文摘要
We investigate the spin dynamics of excitons localized in type I (In,Al)As/AlAs quantum dots with an indirect in momentum space band structure. Polarized selective photoluminescence spectroscopy, i.e. fluorescence line narrowing, under magnetic fields up to 5 T applied in the Faraday geometry is employed. The experiment reveals a cascade spin evolution process of excitons in the indirect band-gap quantum dots: an initial short term spin dynamics associated with excited direct exciton states possessing a large oscillator strength is followed by electron relaxation into the X valley of the Brillouin zone and subsequent long term spin dynamics of indirect excitons. The two step mechanism manifests itself in the distinct features of the magnetic field dependences of photoluminescence: two component recovery of optical orientation, two component linear to circular polarization conversion and the presence of the linear polarization plane rotation. At the same time, suppression of the optical alignment shows one-component behavior governed by the spin dynamics of the indirect exciton states. Within the pseudospin formalism, we derive analytical expressions that quantitatively describe the observed dependences and yield estimates for the anisotropic exchange splitting: 210 μeV for direct excitons and 1.3 μeV for indirect excitons. Further analysis using the density matrix formalism agrees well with the pseudospin model calculations and shows that the finite optical orientation at zero magnetic field is due to comparable magnitudes of the anisotropic splitting of the indirect exciton states and the splitting of the X-valley electron states caused by the hyperfine interaction with nuclei.
