The exceptional point of PT-symmetry metasurface: Topological phase studies and highly sensitive refractive index sensing applications

Exceptional points (EPs) are critical phase points in non-Hermitian systems, exhibiting fantastic physical phenomena and plenty of applications, such as unidirectional reflectionless and ultrahigh-sensitive detection of perturbations. Here, a non-Hermitian metasurface based on multilayers split-ring resonators (SRRs) is proposed with specific EP effects. By changing the angle of the SRRs and adjusting the geometric parameters of the metasurface, EPs are generated with topologically protected 2 pi-phase accumulation. A unique EP effect can be achieved in the THz region, and high-performance sensing of environment refractive index can be realized around the EP position. Therefore, this work demonstrates an EP-based sensing enhancement at non-Hermitian systems compared to Hermitian ones and paves the way for the design of high-performance THz sensors based on topological polaritonic effects.