Electron-phonon coupling in photo-induced phase transitions

Charge transfer and spin conversion compounds are most spectacular examples of systems exhibiting photo-induced phase transitions. In that class of systems, thermal phase transition might also be light (or pressure) induced. Though the driving mechanism of a photo-induced phase transition appears to be electron-phonon coupling, an approach incorporating that coupling within a unified model has not yet been formulated. Two types of treatments, regarding electrons as localised and delocalised are generally considered. We briefly present existing approaches and discuss the main result. The problem of searching common features in thermodynamic properties of such a class of compounds is introduced and the methods in case of charge transfer systems are outlined.