Ghost surface phononic polaritons in ionic-crystal metamaterial

Ghost electromagnetic waves were recently predicted in anisotropic transparent materials by E. Narimanov. In this paper, three ghost surface phonon polaritons (GSPhPs) are predicted at the single oblique surface of layered ionic-crystal metamaterial (ICMM). They propagate along the surface, but their electromagnetic fields in the ICMM sinusoidally oscillate and exponentially attenuate with the distance from the surface. The three GSPhPs are mutually different in character. An additional unique GSPhP is found on the boundary between the effective metal and hyperbolic regions of the ICMM, and its characteristics are as follows: (1) its energy can only conduct outside the ICMM; (2) its wave vector and electric field possess the same direction transverse to the material optical axis. The conditions for the existence of the GSPhPs are discussed. The numerical results were obtained based on ZnS/SiO2 metamaterials.