Guiding Polaritonic Energy and Momentum Through 2D Bravais Lattices

Controlling polariton dispersion facilitates the study of various new physical phenomena, such as Bose-Einstein condensation, polariton lasing, and coherent quantum fluid dynamics, with manual control remaining an area of ongoing exploration. In this work, monolayer MoS₂ based Fabry-Pérot microcavity is used to form polaritons. Five types of Bravais lattices based on polymethyl methacrylate (PMMA) nanopillars are intentionally designed. The energy overlap between the periodic PMMA scattering wave and the polariton establishes a coupling channel that controls the directional flow of polaritonic energy, as demonstrated through angle-resolved reflectance measurements. Back-space image measurements further demonstrate that the dispersion in reciprocal space can be directly and manually tuned, allowing for control over their number and their positions. The coupling between the polariton and PMMA scattering wave is further demonstrated by analyzing the reflectance using temporal coupled-mode theory. The symmetries of 2D Bravais lattices allow the angle between energy and momentum flow to vary widely, and the position of the dispersion branch in a specific direction can be fine-tuned via lattice constant, enabling full-range control over polariton dispersion. This work presents the first theoretical and experimental demonstrations of guiding the direction of polaritonic energy and momentum through Bravais lattice design.