报告题目 (Title)：A new symmetry-mode based descriptor of chirality. Applications to chiral organic-inorganic hybrid metal-halides（一种新的基于对称模式的手性描述符。手性有机-无机杂化金属卤化物的应用）

报告人 (Speaker)：Prof. Branton J. Campbell（Brigham Young University, USA）

报告时间 (Time)：2024年6月20日（周四）19:00-21:00

报告地点 (Place)：校本部 D413

邀请人 (Inviter)：任伟 教授

主办部门：理学院物理系

报告摘要：

A structure is said to be chiral when it has no improper symmetry operations (e.g. mirror planes and inversion centers). Chiral hybrid organic-inorganic perovskites (HOIP) have been reported to possess a variety of exciting electronic, magnetic, optical, and electro-magneto-optical properties, which appear to be the result of chiral framework distortions. The desire to engineer and optimize these properties motivates us to understand how the chiral organic molecule induces chiral distortions of the inorganic framework. Here, we present the use of group-theoretic symmetry-mode analysis to identify and classify all types of chiral distortions of a given layered-HOIP framework. As an example, the single-layered chiral HOIP compound, (MPA)2CuCl4, proves to be incapable of any distortions belonging to its chiral irrep. Remarkably, it exhibits a hybrid-improper chiral distortion, which can be quantified as the pseudo-scalar product ξ=p⋅r of an in-plane ferroelectric moment p and an octahedral rotational moment r. By treating the existence of the chiral molecule as an order parameter θ of the chiral irrep, we obtain an invariant trilinear coupling term of the form θpr in the free energy, which correctly predicts that reversing the chirality of the MPA molecule causes the ferroelectric moment to switch when the sense of the octahedral rotation is fixed.