Goos-Hänchen and Imbert-Fedorov shifts at gradient metasurfaces.

Motivated by recent experimental observation of photonic spin Hall effect at metasurfaces, we study lateral Goos-Hänchen (GH) and transverse Imbert-Fedorov (IF) shifts of an arbitrarily polarized light beam totally reflected from metasurfaces, in terms of stationary phase method and energy flux method. The intriguing phenomenon is that the gradient in phase discontinuity results in anomalous reflection and refraction, and the GH and IF shifts can be thus controlled from negative to positive values by changing the sign of phase discontinuity. The tunable GH and IF shifts have potential applications in nano-optics, with the development of novel functionalities and performances of metasurfaces.