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

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. Halide perovskites feature highly dynamic lattices, but their impact on exciton fine structure remains unexplored. Here, the authors show that these lattices lead to a bright-exciton fine structure gap, enabling observation of quantum beats in a non-uniform ensemble.

Automated summary

The study reports strong bright-exciton fine-structure splitting in solution-processed CsPbI3 perovskite quantum dots, which is robust to quantum dot size and shape heterogeneity and increases with decreasing temperature. The splitting is found to be associated with orthorhombic distortion of the perovskite lattice.