Realizing topologically protected ghost surface polaritons by lattice transformation optics
Phys. Rev. B 112, 085415 – Published 18 August, 2025
DOI: https://doi.org/10.1103/8bjf-py4q
Abstract
While conventional surface waves propagate along the surface and decay perpendicularly from the interface, the ghost surface polaritons show an oblique propagation direction with respect to the interface. Here, we have discovered topologically protected ghost surface polaritons by applying the lattice transformation optics method to gyromagnetic photonic crystals. By introducing the transformation optics method to periodic systems, we develop the lattice transformation optics method to engineer the band structures and propagation directions of the surface polaritons. We show that a simple shear transformation on the square lattice can tailor the propagation directions with ease. A reversed ghost surface polariton is discovered by setting a negative shear coefficient. Interestingly, we find the topological invariant Chern number will change sign when the orientation of the Brillouin zone flips during the transformation. Our findings open up different avenues for studying ghost surface polaritons and provide a general engineering method for periodic systems.
