Mechanism of Circular Dichroism in Chiral 2D Halide Perovskites and Chiroptical Properties of Perovskite Nanocrystals

A key motivator for research in hybrid organic-inorganic metal halide perovskites (HOIPs) is the potential to combine distinct characteristics of the inorganic and organic constituents to elicit desirable functional properties. For example, incorporation of chiral organic cations into layered 2D halide perovskites has been shown to result in structural chirality transfer to the inorganic layers, leading to Rashba/Dresselhaus-like spin-splitting while at the same time leading to the emergence of chiroptical effects such as circular dichroism (CD) [1,2].<br/><br/>In the first part of this talk, we address the following question: In chiral 2D perovskites, what connection exists, if any, between the spin textures that emerge by virtue of structural chirality transfer, and the emergence of chiroptical properties associated with the band edge exciton transitions? We explore this question utilizing an effective mass theory model parameterized by hybrid density functional theory calculations [3]. The model accounts for the mixed parity of the band edge states resulting from polar distortions and includes the effects of Rashba-like spin-splitting via an effective exchange interaction. We develop analytical expressions for the exciton fine structure, the electric and magnetic dipole transition matrix elements, and show a direct connection between particular spin textures and the emergence of CD in chiral 2D perovskites [3].<br/><br/>In the second part of the talk, we generalize the model and apply it to perovskite nanocrystals. We will discuss the mechanisms by which chiroptical properties can occur in perovskite nanocrystals, e.g., as reported in Ref. [4], with [5] or without polar distortions, and we will discuss the characteristics and magnitude of the chiroptical effects associated with the various mechanisms.<br/><br/><b>Acknowledgements</b><br/>This work was supported as part of 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.<br/><br/><br/>1. M. K. Jana, <i>et al</i>., Organic-to-inorganic structural chirality transfer in a 2D hybrid perovskite and impact on Rashba-Dresselhaus spin-orbit coupling, <i>Nat. Commun.,</i> 11:4699, (2020).<br/>2. M. K. Jana, <i>et al</i>., Structural descriptor for enhanced spin-splitting in 2D hybrid perovskites, <i>Nat. Commun.,</i> 12:4982, (2021).<br/>3. P. C. Sercel, M. P. Hautzinger, R. Song, V. Blum, and M. C. Beard, Mechanism of circular dichroism in chiral perovskites, in preparation, (2024).<br/>4. V. Oddi <i>et al</i>., ACS Nano, DOI: 10.1021/acsnano.4c04392 (2024).<br/>5. M. W. Swift and John L. Lyons,<i> Chem. Mater.</i>, 35, 9370 (2023).