Topological Refraction in Kagome Split-Ring Photonic Insulators.

Abstract

A valley-Hall-like photonic insulator based on Kagome split-ring is proposed. Theoretical analysis and numerical calculations illustrate that symmetry can be broken not only by global rotation but also individual rotation of the split rings, providing topological phase transitions. Furthermore, refraction of the edge state from the interface into the background space at Zigzag termination is explored. It is shown that positive/negative refraction of the outgoing beam depends on the type of valley (K or ), from which the edge state is projected. These results provide a new way to manipulate terahertz wave propagation and facilitate the potential applications in directional collimation, beam splitting, negative refraction image, etc.