phononexcitons

Phonon-excitons, also known as exciton-polaritons or more generally as mixed quasi-particles, are composite particles that arise from the strong coupling between excitons and photons within a material. An exciton is a bound state of an electron and an electron hole, representing an excited state of a semiconductor or insulator. A photon is a quantum of electromagnetic radiation, a particle of light. When the energy and momentum of an exciton and a photon match, and the coupling strength is sufficiently large, they can no longer be considered independent entities. Instead, they hybridize to form a new quasi-particle, the phonon-exciton.

This hybridization leads to a significant modification of the optical properties of the material. Specifically, the dispersion relation, which describes the relationship between the energy and momentum of the quasi-particle, exhibits a characteristic "U" or "S" shape known as a Rabi splitting. This splitting indicates the formation of two new energy branches, an upper polariton branch and a lower polariton branch, separated by the coupling strength.

The study of phonon-excitons is important for understanding light-matter interactions in various condensed matter systems. They have been observed and investigated in a wide range of materials, including semiconductors, organic molecules, and topological insulators. Their unique properties make them potential candidates for applications in advanced optical devices, such as low-threshold lasers, optical switches, and quantum information processing. Research continues to explore their fundamental physics and potential technological uses.