Topologically Protected and Highly Localized Surface Waves in Gyro-Electromagnetic Metamaterials

Topological insulators are internally insulating but allow topologically protected surface waves at the boundary. In this work, the photonic analogue of topologically protected surface states in gyro-electromagnetic metamaterials are discovered. It is analytically and numerically demonstrated that the surface waves appear not only in the k-space common gap regions between the bulk states of the metamaterials and the vacuum state, but even can exist in an infinitely extended k-space. Such surface waves have extremely large wave vectors along the propagation direction with high field localization on the surface. It is believed that the high field localization of surface waves could improve the compactness of photonic devices and facilitate the integration of photonic circuits.