Tuning across vibrational light-matter coupling regimes in van der Waals crystals

The strong light-matter coupling regime is achieved when the dipolar transition of a material hybridizes with a confined optical resonance. In this regime new polaritonic eigen-states are formed, with shared optical and material character. While such states have long been studied in the context of non-linear optics, recent experiments reported dramatic modifications of physico-chemical properties of materials upon the formation of polaritonic states. These reports range from enhanced energy and charge transfers, to the modification of chemical reaction pathways.

Here we study the formation of phonon-polaritons in the vibrational strong coupling regime, where hyperbolic phonons of van der Waals materials hybridize with optical resonances. This leads to a rich interplay between coupling strength, photonic mode structure and crystal anisotropy, as well as a dissipative transition between different light-matter coupling mechanisms, as theoretically predicted by Balasubrahmaniyam et al. [1].

[1] M. Balasubrahmaniyam, C, Genet, and T, Schwartz, Phys. Rev. B 103, L241407 (2022).