Terahertz non-Hermitian topological metasurface with switchable characteristics of transmission and reflection

With the increasing exploration of non-Hermitian systems, the topological properties of exceptional points (EPs) in non-Hermitian metasurfaces have garnered significant attention. This paper investigates a VO2-based non-Hermitian topological metasurface within the terahertz (THz) frequency domain. We achieve switching between transmission and reflection by actively controlling the conductivity of vanadium dioxide (VO2), thereby realizing dual-channel EPs simultaneously. Notably, there is a consistent 2π phase accumulation around the EPs, irrespective of the closure path. Furthermore, we demonstrate that EP can also be observed by varying the incidence angle. The examination of dual-channel EPs and their topological properties offers a promising avenue for the development of topological devices and future applications in optical transmission and modulation.