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Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI3 perovskite quantum dots

Abstract

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 CsPbI3 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.

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Fig. 1: Principle of FSS and sample information.
Fig. 2: Quantum beats and FSS in ensemble CsPbI3 QD films.
Fig. 3: Temperature-dependent FSS in CsPbI3 QDs.
Fig. 4: Temperature-dependent lattice distortion in CsPbI3 QDs.
Fig. 5: Quasi-cubic model calculation and fine-structure gap.
Fig. 6: Calculated temperature- and size-dependent FSS.

Data availability

All data are available in the main text or the Supplementary Information and can be obtained upon request from K.W. (kwu@dicp.ac.cn). They are also available at figshare, https://figshare.com/articles/figure/20220725-Figures_in_paper_pptx/20365515. Source data are provided with this paper.

Code availability

Custom software developed for the theoretical modelling associated with this study is available for verification purposes upon request from P.C.S. (pcsercel@gmail.com).

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Acknowledgements

We thank Y. Zhao, W. Liu and Q. Jiang for TEM measurements, C. Wang for X-ray diffraction measurements and P. Guo for discussions on X-ray diffraction refinement. K.W. acknowledges financial support from the Chinese Academy of Sciences (YSBR-007), the Ministry of Science and Technology of China (2018YFA0208703), the National Natural Science Foundation of China (22173098) and Dalian Institute of Chemical Physics (DICP I201914). All the theoretical calculations of exciton fine structure and simulations of QD transient absorption were supported by the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the US Department of Energy.

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K.W. and Y.H. conceived the idea and initiated the study. K.W. supervised and designed the project. Y.H. synthesized the samples and measured their spectroscopy. W.L. made the X-ray diffraction Rietveld refinement. X.L., Y.L., F.S. and F.Z. helped with experiments or data analysis. P.C.S. developed the theoretical model for exciton fine structure and transient absorption. K.W., Y.H. and P.C.S. wrote the manuscript with contributions from all authors.

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Correspondence to Peter C. Sercel or Kaifeng Wu.

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Han, Y., Liang, W., Lin, X. et al. Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI3 perovskite quantum dots. Nat. Mater. (2022). https://doi.org/10.1038/s41563-022-01349-4

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