DeCrescent Ryan A, Venkatesan Naveen R, Dahlman Clayton J, Kennard Rhys M, Zhang Xie, Li Wenhao, Du Xinhong, Chabinyc Michael L, Zia Rashid, Schuller Jon A
Department of Physics, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Materials Department, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Sci Adv. 2020 Feb 7;6(6):eaay4900. doi: 10.1126/sciadv.aay4900. eCollection 2020 Feb.
Light-matter interactions in semiconductors are uniformly treated within the electric dipole approximation; multipolar interactions are considered "forbidden." We experimentally demonstrate that this approximation inadequately describes light emission in two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs), solution processable semiconductors with promising optoelectronic properties. By exploiting the highly oriented crystal structure, we use energy-momentum spectroscopies to demonstrate that an exciton-like sideband in 2D HOIPs exhibits a multipolar radiation pattern with highly directed emission. Electromagnetic and quantum-mechanical analyses indicate that this emission originates from an out-of-plane magnetic dipole transition arising from the 2D character of electronic states. Symmetry arguments and temperature-dependent measurements suggest a dynamic symmetry-breaking mechanism that is active over a broad temperature range. These results challenge the paradigm of electric dipole-dominated light-matter interactions in optoelectronic materials, provide new perspectives on the origins of unexpected sideband emission in HOIPs, and tease the possibility of metamaterial-like scattering phenomena at the quantum-mechanical level.
半导体中的光与物质相互作用在电偶极近似下得到统一处理；多极相互作用被视为“禁戒”。我们通过实验证明，这种近似不足以描述二维（2D）有机-无机杂化钙钛矿（HOIPs）中的光发射，HOIPs是具有良好光电特性的可溶液加工半导体。通过利用高度取向的晶体结构，我们使用能量-动量光谱学来证明二维HOIPs中类似激子的边带表现出具有高度定向发射的多极辐射模式。电磁和量子力学分析表明，这种发射源于由电子态的二维特性引起的面外磁偶极跃迁。对称性论证和温度相关测量表明存在一种在很宽温度范围内起作用的动态对称性破缺机制。这些结果挑战了光电子材料中以电偶极为主导的光与物质相互作用的范式，为HOIPs中意外边带发射的起源提供了新视角，并揭示了量子力学层面类似超材料散射现象的可能性。
