Li Shunran, Xu Xian, Kocoj Conrad A, Zhou Chenyu, Li Yanyan, Chen Du, Bennett Joseph A, Liu Sunhao, Quan Lina, Sarker Suchismita, Liu Mingzhao, Qiu Diana Y, Guo Peijun
Department of Chemical and Environmental Engineering, Yale University, New Haven, CT, USA.
Energy Sciences Institute, Yale University, West Haven, CT, USA.
Nat Commun. 2024 Mar 22;15(1):2573. doi: 10.1038/s41467-024-46851-2.
In two-dimensional chiral metal-halide perovskites, chiral organic spacers endow structural and optical chirality to the metal-halide sublattice, enabling exquisite control of light, charge, and electron spin. The chiroptical properties of metal-halide perovskites have been measured by transmissive circular dichroism spectroscopy, which necessitates thin-film samples. Here, by developing a reflection-based approach, we characterize the intrinsic, circular polarization-dependent complex refractive index for a prototypical two-dimensional chiral lead-bromide perovskite and report large circular dichroism for single crystals. Comparison with ab initio theory reveals the large circular dichroism arises from the inorganic sublattice rather than the chiral ligand and is an excitonic phenomenon driven by electron-hole exchange interactions, which breaks the degeneracy of transitions between Rashba-Dresselhaus-split bands, resulting in a Cotton effect. Our study suggests that previous data for spin-coated films largely underestimate the optical chirality and provides quantitative insights into the intrinsic optical properties of chiral perovskites for chiroptical and spintronic applications.
在二维手性金属卤化物钙钛矿中，手性有机间隔物赋予金属卤化物亚晶格结构和光学手性，从而能够精确控制光、电荷和电子自旋。金属卤化物钙钛矿的手性光学性质已通过透射圆二色光谱法测量，这需要薄膜样品。在此，通过开发一种基于反射的方法，我们表征了典型二维手性溴化铅钙钛矿的本征、圆偏振依赖复折射率，并报告了单晶的大圆二色性。与从头算理论的比较表明，大圆二色性源于无机亚晶格而非手性配体，是一种由电子-空穴交换相互作用驱动的激子现象，这种相互作用打破了Rashba-Dresselhaus分裂能带之间跃迁的简并性，从而产生了科顿效应。我们的研究表明，之前旋涂膜的数据在很大程度上低估了光学手性，并为手性钙钛矿在手性光学和自旋电子学应用中的本征光学性质提供了定量见解。
