Description
Polaritonic van der Waals metasurfaces provide a versatile platform for compact metaphotonic devices, including topological photonic circuitry, chiral light sources, and nonlinear optics. Their functionality relies on the coexistence of strong exciton-photon coupling, large oscillator strengths, deeply subwavelength thicknesses, and symmetry-controlled band topology. However, the design of such metasurfaces is commonly based on simplified tight-binding or plane-wave models, which often treat radiative losses, excitonic degrees of freedom, and light-matter coupling phenomenologically.
We develop a general semiclassical model for exciton-polariton modes in resonant polaritonic metasurfaces. The theory combines a Green-function formulation of quasiguided photonic modes with an excitonic envelope-function description, including periodic modulation of the exciton center-of-mass motion. By eliminating nonresonant radiative photonic and excitonic harmonics, we derive an effective non-Hermitian Hamiltonian for the resonant guided-mode harmonics. The model explicitly captures radiative losses, near-field and radiative exciton-photon coupling, multipolar selection rules, and finite-wave-vector corrections near the Brillouin-zone center.
We validate the Hamiltonian using a $C_{6v}$-symmetric bulk WS$_2$ metasurface and compare its predictions with rigorous coupled-wave analysis and full-wave FEM simulations for both TE- and TM-polarized excitation. The model reproduces the formation of multiple exciton-polariton branches and reveals their multipolar composition. We then apply the theory to topological polaritonics and show that the dipole-quadrupole band inversion is governed by a simple analytical condition involving the first and third Fourier components of the dielectric modulation. Beyond the conventional breathing-honeycomb transition, this criterion predicts an additional shape-controlled topological phase. Full-wave simulations confirm the associated band inversion and demonstrate photonic and polaritonic edge states at an interface between trivial and topological domains. These results establish a general design framework for strongly coupled topological van der Waals metasurfaces.
| I am the presenting author | Yes |
|---|