A polariton is a hybrid excitation resulting from strong light–matter coupling. The magneto-transport measurements have now revealed the crucial role played by its electronic component.

Here, the authors demonstrate that the dispersion of hyperbolic phonon polaritons can be controlled using the permittivity changes inherent in the different phases of phase change materials. This enables direct launching, reflection, transmission and refraction at the phase change material domain boundaries.

A part-light, part-matter exciton-polariton topological insulator is created in an array of semiconductor microcavities.

Driven-dissipative microcavity polariton experiments find superfluid-like behaviour but the intuition developed from equilibrium systems cannot be straightforwardly applied. Juggins et al. show coherently-driven polaritons are not superfluid and earlier observations instead arise from a distinct rigid state.