Photoinduced phase transition towards lower symmetry in functionnal materials monitored by time-resolved x-ray diffraction

Photoinduced phase transitions have open a wide field of investigation for functional materials, where a single laser shot can drive a macroscopic phase transition, which may persist at room temperature. Usually, thermal phase transition on warming or photoinduced phase transition processes occur from a low symmetry towards a higher symmetry phase, due to entropy consideration. We have recently shown that coupled changes of electronic state and symmetry at thermal equilibrium allows for the appearance of high temperature low symmetry phases, which we observed in a spin-crossover material. We propose to study by time-resolved x-ray diffraction the dynamics beyond photoinduced change of spin state and symmetry breaking, for understanding how the photoinduced change of spin state drives symmetry-breaking. Photoinduced symmetry breaking represents a fascinating perspective, as many functions are related to ordering phenomena, such as ferromagnetism, ferroelectricity of ferroelasticity.