Criterion for photonic topological transition in two-dimensional heterostructures

The anisotropic van der Waals material alpha-MoO3 has recently attracted considerable attention because of the ability to support ellipse and hyperbolic phonon polari-tons with extreme field confinement and long lifetimes, which can be used in topological transition and trans-formation polaritonics. However, the dispersion theory of some phonon polaritons in complex heterojunctions often requires tedious computation, which makes it difficult to sim-ply judge and analyze the physical process of the photonic topological transition. Here we obtain the equivalent permit-tivity distribution of two-dimensional (2D) heterostructures by the effective medium theory and analyze the rotation -induced topological transitions and stack-dependent topo-logical transitions of phonon polaritons. Unlike the previous discussion, we can predict the topological transition points by a parameter epsilon x/y(i.e., the permittivity ratio along the in -plane crystal axis of the equivalent medium) and design precisely the phonon polaritons in the stacked materials by controlling the equivalent permittivity after simple cal-culation. The feasibility of the effective medium theory is verified based on the 2D approximation model and the non -2D approximation model under the limit of an ultrathin slab. Meanwhile, we compare the field distributions and dis-persions of the 2D heterostructures and the corresponding equivalent structure. The simulation suggests that the ellip-tic/hyperbolic responses of the stacked materials depend on the sign of epsilon x/y. The new, to the best of our knowledge, method not only provides an easier and clearer criterion for the study of photonic topological transition in anisotropic polaritons, but also shows great potential in designing some multilayer 2D heterostructures.(c) 2022 Optica Publishing Group

Automated summary

This study obtains the equivalent permittivity distribution of 2D heterostructures using the effective medium theory and analyzes the rotation-induced topological transitions and stack-dependent topological transitions of phonon polaritons. The topological transition points can be predicted by a parameter epsilon x/y, and the phonon polaritons in stacked materials can be precisely designed by controlling the equivalent permittivity. The feasibility of the effective medium theory is verified and the field distributions and dispersions of the 2D heterostructures are compared with the corresponding equivalent structure. The study provides a simpler and clearer criterion for the study of photonic topological transition in anisotropic polaritons and shows great potential in designing multilayer 2D heterostructures.