Nonreciprocal Goos-Hänchen shift by topological edge states of a magnetic photonic crystal.

We demonstrate that a topological edge state can enhance the Goos-Hänchen (GH) shift on the interface of a magnetic photonic crystal (MPC) fabricated by ferrite rings in a square lattice. The GH shift is nonreciprocal because of the time reversal symmetry breaking, and the shift is negative, which is associated with the incident angles and direction of bias DC magnetic field. In particular, the nonreciprocal GH shift presents at normal incidence, and is further verified by experiments. The nonreciprocal negative GH shifts provide a new way to control the flow of light, which could be applied to sensing and even the slow light waveguide to trap the light.