Photo-Induced Phase Transition in an Electron–Lattice Correlated System –Future Role of a Time-Resolved X-ray Measurement for Materials Science–

The search for materials that show a phase transition triggered by weak external stimulation of light is an important and attractive target for photonic and materials science. We review experimental evidence indicating that photo-injected local excitation can really trigger an electron–lattice coupled cooperative phenomenon called photo-induced phase transition (PIPT). We discuss the dynamical nature of electron (spin)–lattice-coupled changes in π-conjugated polymer crystals, organic transition metal complexes, and organic A 2 B charge transfer complexes. We also review the development of ultra-fast X-ray technology in collaboration with work in the fields of quantum electronics and synchrotron radiation, which are essential for the promotion of the future study of PIPT.