Hybrid waves localized at hyperbolic metasurfaces

The authors show theoretically that hyperbolic metasurfaces support simultaneous propagation of both quasi-TE and quasi-TM plasmon surface modes of ``hybrid''' polarization at the same frequency --- a two-dimensional analog of D'yakonov surface waves. The shape of their equal-frequency contours depends drastically on the frequency and changes from elliptical to hyperbolic, and so a topological transition takes place.