Routing Optical Spin and Pseudospin with Metasurfaces

Controlling and guiding optical spins and pseudospins over an interface is of great importance in the emerging fields of spintronics and valleytronics, holding the promise for new degrees of freedom in the quest for efficient information transport. Here we explore the general possibilities offered by metasurfaces to route optical momentum, spin and helicity through surface waves. We show how anisotropy and bianisotropy can be engineered to impart extreme directionality to local spin excitations. While most previous works have focused on out-of-plane spins, in-plane excitations have become particularly important for valleytronic applications relying on two-dimensional materials, and they offer specific challenges addressed here with suitably engineered nonlocality in metasurfaces.