Polariton
Polaritons are quasiparticles in crystals. They are an expression of the common quantum phenomenon known as level repulsion also known as the anti-crossing principle. Polaritons describe the crossing of the dispersion of light with any interacting resonance or quasi-particle.
Thus, a polariton is the result of the mixing of a photon with an excitation of a material. The most discussed types of polaritons are phonon-polaritons resulting from coupling of a photon with a phonon and exciton-polaritons (with exciton).
Whenever the polariton picture is valid, the model of photons in crystals should be rejected. A major feature of polaritons is a strong dependency of the propagation speed of light through the crystal on the frequency. For exciton-polaritons rich experimental results on various aspects have been gained in copper (I) oxide.
References
- U. Fano: Atomic Theory of Electromagnetic Interactions in Dense Materials, Phys.Rev. 103 (1956), 1202.
- J.J. Hopfield: Theory of the Contribution of Excitonsto the Complex Dielectric Constant of Crystals, Phys.Rev. 112 (1958), 1555.
