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

TL;DR

This study demonstrates significant exciton splitting and quantum beating in CsPbI3 perovskite quantum dots caused by lattice distortion, observable at ensemble level and across various temperatures, advancing quantum information applications.

Contribution

It reveals a robust exciton fine-structure splitting in CsPbI3 QDs due to orthorhombic lattice distortion, measurable at ensemble level and at higher temperatures than previously possible.

Findings

Bright-exciton FSS up to 1.6 meV observed

FSS is stable despite size and shape heterogeneity

FSS increases as temperature decreases

Abstract

Anisotropic exchange-splitting in semiconductor quantum dots (QDs) results in bright-exciton fine-structure-splitting (FSS) important for quantum information processing. Direct measurement of FSS usually requires single/few QDs at liquid-helium temperatures, because of its sensitivity to QD size and shape, whereas measuring and controlling FSS at an ensemble-level seem to be impossible unless all the dots are made to be nearly the same. Here we report strong bright-exciton FSS up to 1.6 meV in solution-processed CsPbI3 perovskite QDs, manifested as quantum beats in ensemble-level transient absorption at liquid-nitrogen to room temperatures. The splitting is robust to QD size and shape heterogeneity, and increases with decreasing temperature, pointing towards a mechanism associated with orthorhombic distortion of perovskite lattice. Effective-mass-approximation calculations reveal an intrinsic "fine-structure gap" that agrees well with the observed FSS. This gap stems from an avoided crossing of bright-excitons confined in orthorhombically-distorted QDs that are bounded by the pseudocubic {100} family of planes.