Achieving Higher-Order Exceptional Points in a Terahertz Metasurface.

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.