Intrinsic Rashba Effect in Stable Configurations of Two-Dimensional (PEA)₂PbI₄

Halide perovskites (HPs) are crystalline solids that feature a unique softness, absent in conventional semiconducting materials. In recent years, this softness has been pivotal to many properties in these materials, in both static and dynamic regimes. Here, we focus on the two-dimensional (2D) (PEA)2PbI4 crystal. We employ extensive density functional theory calculations and structural analysis to uncover a rich mosaic of ground-state configurations, identifying several stable configurations with distinct electronic properties. Our study uncovers an intrinsic Rashba effect within a structure traditionally considered as globally centrosymmetric, presenting a challenge to conventional understanding in the field. The observed effect emerges from a local symmetry-breaking induced by specific spatial orientations of the organic PEA molecules. This intrinsic Rashba effect, observed in select configurations, underscores the nuanced symmetrical complexities of 2D HPs and highlights their potential for spin-related applications. Additionally, our investigation demonstrates the exceptional flexibility of 2D HPs, as evidenced by an observed significant tolerance toward single-molecule rotations. This flexibility suggests potential pathways for smoother transitions between different molecular domains within these materials. Overall, our findings emphasize the intricate interplay between the organic/inorganic counterparts and the electronic properties in 2D HPs, paving the way for further exploration and exploitation of their unique characteristics in various optoelectronic and spintronic applications.卤化物钙钛矿（Halide perovskites, HPs）是一类具备独特柔软性的晶体固体，而该特性在传统半导体材料中并不存在。近年来，这种柔软性在该类材料的静态与动态性能调控中均发挥了关键作用。本文聚焦于二维（2D）(PEA)₂PbI₄晶体。我们通过大规模密度泛函理论（density functional theory）计算与结构分析，揭示了其丰富多样的基态构型组合，并鉴定出若干具有独特电子性质的稳定构型。本研究在以往被认为是全局中心对称的结构中，发现了一种本征拉什巴效应（Rashba effect），这对该领域的传统认知构成了挑战。该效应源于有机PEA分子的特定空间取向所引发的局域对称性破缺。在部分特定构型中观测到的本征拉什巴效应，凸显了二维卤化物钙钛矿精妙复杂的对称特性，也彰显了其在自旋相关应用中的潜力。此外，我们的研究证实了二维卤化物钙钛矿具备优异的结构灵活性：实验观测到其对单分子旋转具备极高的容忍度。这种灵活性为该类材料中不同分子域之间实现更平滑的过渡提供了可行路径。综上，本研究结果凸显了二维卤化物钙钛矿中有机/无机组分与电子性质之间的复杂相互作用，为进一步探索并利用其独特特性应用于各类光电子与自旋电子学领域铺平了道路。