Achieving Higher-Order Exceptional Points in a Terahertz Metasurface
Peng Fu, Pai Peng, Wenze Lan, Shuo Du, Jiawei Shao, Leyong Hu, Chensheng Li, Yuyang Zhang, Zi‐Lan Deng, Baoli Liu, Luyi Yang, Changzhi Gu
Abstract
Exceptional points (EPs) are unique features of non-Hermitian systems, where eigenvalues and eigenvectors coalesce, enabling functionalities such as ultrasensitive sensing and topological energy transfer. While higher-order EPs have been studied in microdisk cavities and circuits, their realization in metasurfaces has been challenging. In this work, we demonstrate the first realization of a third-order EP (EP3) in terahertz metasurfaces by tuning the near-field interaction between three gold split-ring resonators. This transition from second-order EP (EP2) to EP3 is validated by the simultaneous collapse of three eigenvalues and eigenfunctions. Using a global optimization algorithm combined with neural networks, we optimized the condition for EP3 in a high-dimensional parameter space. Our terahertz metasurface is suitable for ultrasensitive biosensing applications, offering a novel mechanism for EP3 realization and paving the way for advanced optical communication and sensing systems.