Symmetry-driven directional selectivity of diffraction-free propagation in hyperbolic metasurfaces.

Hyperbolic metasurfaces with hyperbolic dispersion have gained significant attention due to their unprecedented capabilities to manipulate the propagation of surface plasmon polaritons, such as non-divergent diffraction and polarization-controlled signal routing based on the plasmonic spin Hall effect. However, thus far, selective routing of surface waves has only been observed with the mechanism of plasmonic spin-orbit coupling, which depends on the polarization of light and the hyperbolic iso-frequency contours. Here, we propose and experimentally demonstrate symmetry-dependent selective electric and magnetic surface wave excitation around the geometric phase transition frequency with coexisting transverse electric and transverse magnetic polarization states. Effective medium theory and S-parameter retrieval process are further utilized to analyze the electromagnetic responses and dispersion characteristics of the designed asymmetric hyperbolic metasurface. These results open up a new avenue, to our knowledge, to realize integrated plasmonic devices, holding potential for applications in areas including imaging, sensing, and quantum information science.