Maximum helical dichroism enabled by an exceptional point in non-Hermitian gradient metasurfaces

Xiao Li; Chuanjie Hu; Yuan Tian; Youwen Liu; Huanyang Chen; Yadong Xu; Ming-Hui Lu; Yangyang Fu

doi:10.1016/j.scib.2023.09.028

Maximum helical dichroism enabled by an exceptional point in non-Hermitian gradient metasurfaces

Sci Bull (Beijing). 2023 Nov 15;68(21):2555-2563. doi: 10.1016/j.scib.2023.09.028. Epub 2023 Sep 23.

Authors

Xiao Li¹, Chuanjie Hu², Yuan Tian³, Youwen Liu⁴, Huanyang Chen², Yadong Xu⁵, Ming-Hui Lu³, Yangyang Fu⁶

Affiliations

¹ College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China; Key Laboratory of Aerospace Information Materials and Physics, Ministry of Industry and Information Technology, Nanjing 211106, China.
² Department of Physics, Xiamen University, Xiamen 361005, China.
³ National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China.
⁴ College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China; Key Laboratory of Aerospace Information Materials and Physics, Ministry of Industry and Information Technology, Nanjing 211106, China. Electronic address: ywliu@nuaa.edu.cn.
⁵ School of Physical Science and Technology & Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006, China. Electronic address: ydxu@suda.edu.cn.
⁶ College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China; Key Laboratory of Aerospace Information Materials and Physics, Ministry of Industry and Information Technology, Nanjing 211106, China; State Key Laboratory of Mechanics and Control for Aerospace Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China. Electronic address: yyfu@nuaa.edu.cn.

PMID: 37798177
DOI: 10.1016/j.scib.2023.09.028

Abstract

Helical dichroism (HD) utilizing unbounded orbital angular momentum degree of freedom, has provided an important means of exploring chiral effects in diverse wave systems, surpassing the two-state constraint in circular dichroism that relies on intrinsic spin. However, the naturally feeble chiral signals that arise during wave-matter interactions pose significant challenges to the effective enlargement of HD. Here, we introduce a new paradigm for realizing maximum HD through non-Hermitian gradient metasurfaces by engineering a chiral exceptional point (EP) in intrinsic topological charge. The non-Hermitian gradient metasurfaces are empowered by the asymmetric coupling feature at the EP, enabling flexible construction to realize versatile chirality control in extreme circumstances where one chiral vortex is totally reflected and the opposite counterpart is completely absorbed or transmitted into the customized vortex modes. As the manifestation of the maximum HD, we present the first experimental demonstration of perfect chirality-selected vortex transmission in acoustics. Our findings open new venues to achieve maximum chirality and explore chiral physics of wave-matter interactions, which can boost many vortical applications in asymmetric chirality manipulation, one-way propagation, and information multiplexing.

Keywords: Acoustic waves; Exceptional point; Helical dichroism; Maximum chirality; Non-Hermitian metasurfaces.