Topological transitions in arrays of dipoles coupled to a cavity waveguide

Abstract

Topological valley-Hall edge states have been realized in a variety of photonic structures across the electromagnetic spectrum because they can be easily engineered by breaking certain lattice symmetries. However, the valley-Chern numbers that characterize the topological phase are usually fixed by the symmetry-breaking perturbation and therefore the valley-Hall edge states are forced to propagate in a fixed direction. Here we consider a kagome metasurface comprised of a subwavelength array of dipole emitters/antennas, and we unveil that one can modify the geometrical and topological properties of the polaritons by structuring the local photonic environment. As a proof of concept, we show that one can induce topological transitions via accidental Dirac points by embedding the metasurface inside a cavity waveguide. Varying the cavity width modifies the nature of the dipole-dipole interactions which enables one to manipulate the Berry curvature and invert the valley-Chern numbers without inverting the symmetry-breaking perturbation. Consequently, we demonstrate that one can switch the chirality of the polariton valley-Hall edge states by varying only the cavity width. This alternative approach to engineering topological transitions via structuring the photonic environment could also have implications for other topological phases such as photonic higher-order topological insulators.