Topological phonon-polariton funneling in midinfrared metasurfaces.

Topological photonics offers enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding of topological states of light. By combining the strong coupling between topological photons with phonons in hexagonal boron nitride (hBN), we demonstrate a platform to control and guide hybrid states of light and lattice vibrations. The observed topological edge states of phonon-polaritons are found to carry nonzero angular momentum locked to their propagation direction, which enables their robust transport. Thus, these topological quasiparticles enable the funneling of infrared phonons mediated by helical infrared photons along arbitrary pathways and across sharp bends, thereby offering opportunities for applications ranging from Raman and vibrational spectroscopy with structured phonon-polaritons to directional heat dissipation.