Photonic crystals for controlling strong coupling in van der Waals materials.

The design of photonic structures plays a crucial role in the engineering of light-matter interactions. Planar microcavities have been widely used to establish strong light-matter coupling in semiconductor quantum wells, leading to intense research on exciton-polariton systems in the past few decades. However, planar cavities are limited in material compatibility, inflexible for mode engineering, and bulky for integration. Here we demonstrate dielectric slab photonic crystals as a flexible and compact platform for polaritons, where excitons are strongly coupled to photons confined in the leaky modes of the slab. We show our structure is well-suited for van der Waals materials, features unusual adjustable dispersions, and allows for multi-wavelength operation on a single chip.