Wikipedia
Exciton-polaritons
Exciton-polaritons are a type of polariton quasiparticle arising from strong coupling of excitons (bulk or quantum well) and photons. Especially strong coupling occurs in semiconductor microcavities where polaritons can be quantized. Cavity exciton-polaritons are characterized by a non-parabolic dispersion, a light effective mass and a capacity to interact with each other and with the environment (including phonons, which provide thermalization). Exciton-polaritons are composite bosons and can be observed to form Bose-Einstein condensates.