Han Yaoyao, Liang Wenfei, Lin Xuyang, Li Yulu, Sun Fengke, Zhang Fan, Sercel Peter C, Wu Kaifeng
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China.
University of Chinese Academy of Sciences, Beijing, China.
Nat Mater. 2022 Nov;21(11):1282-1289. doi: 10.1038/s41563-022-01349-4. Epub 2022 Sep 8.
Anisotropic exchange splitting in semiconductor quantum dots results in bright-exciton fine-structure splitting important for quantum information processing. Direct measurement of fine-structure splitting usually requires single/few quantum dots at liquid-helium temperature because of its sensitivity to quantum dot size and shape, whereas measuring and controlling fine-structure splitting at an ensemble level seem to be impossible unless all the dots are made to be nearly identical. Here we report strong bright-exciton fine-structure splitting up to 1.6 meV in solution-processed CsPbI perovskite quantum dots, manifested as quantum beats in ensemble-level transient absorption at liquid-nitrogen to room temperature. The splitting is robust to quantum dot size and shape heterogeneity, and increases with decreasing temperature, pointing towards a mechanism associated with orthorhombic distortion of the perovskite lattice. Effective-mass-approximation calculations reveal an intrinsic 'fine-structure gap' that agrees well with the observed fine-structure splitting. This gap stems from an avoided crossing of bright excitons confined in orthorhombically distorted quantum dots that are bounded by the pseudocubic {100} family of planes.
半导体量子点中的各向异性交换分裂导致了对量子信息处理至关重要的明亮激子精细结构分裂。由于精细结构分裂对量子点尺寸和形状敏感，直接测量通常需要在液氦温度下的单个/少数量子点，而在系综水平上测量和控制精细结构分裂似乎是不可能的，除非所有量子点都几乎相同。在此，我们报道了溶液法制备的CsPbI钙钛矿量子点中高达1.6 meV的强明亮激子精细结构分裂，在液氮到室温的系综水平瞬态吸收中表现为量子拍。这种分裂对量子点尺寸和形状的不均匀性具有鲁棒性，并且随着温度降低而增加，这指向一种与钙钛矿晶格正交畸变相关的机制。有效质量近似计算揭示了一个与观察到的精细结构分裂很好吻合的本征“精细结构能隙”。这个能隙源于被正交畸变量子点限制的明亮激子的避免交叉，这些量子点由伪立方{100}面族界定。
