Photo-Induced Elastic Cooperativity in Bi-stable Volume-Changing Materials – ELASTICA

ELASTICA is a fundamental research project aiming at thorough understanding, and ultimately the control, of “Photo-induced elastic cooperativity in bi-stable volume-changing materials”. Unprecedented opportunities have emerged for impacting macroscopic states of materials with a femtosecond (fs) laser pulse, allowing to reach another electronic and/or structural order, thereby directing material functionality. The field of photo-induced phase transformations proliferates rapidly on many and diverse directions, from the melting of charge and/or spin order in electron correlated materials to molecular switching in the solid state. Our project brings the photo-switching of materials into a new perspective, different from the common approach focused on electron and optical phonon dynamics at ultrafast timescales. Instead, we focus on crystal deformations occurring on the acoustic timescale. This is determined by the speed of sound and the size of the studied system, so generally slower, but also ultrafast when nano-scale materials are dealt with. On the one hand, elastically driven cooperative response during the propagation of a non-linear coherent strain wave coupled to the order parameter field has been recently reported by our group in a volume-changing material. The medium exerts positive feedback which significantly amplifies the transformation ratio and extends the lifetime of the photo-induced state. On the other hand, a severe limitation to technological applications has been thus far the transient nature of photo-induced states, very often not surviving the fast relaxation of excited electrons and coherent (optical) phonons. It is of paramount importance from the fundamental stand point, as well as for the control of non-volatile information and energy storage, to explore how the states induced by an ultra-short laser pulse can become persistent. A promising route is the stabilization of the non-equilibrium macroscopic states by controllably generating the crystal deformation, such as volume change in thermodynamically bi-stable regime. The establishment of the macroscopic crystal deformation is necessary to attain a switched state that is robust against the thermal noise of environment. The main goal of ELASTICA is to thoroughly investigate the underlying elastic cooperative mechanisms, and ultimately to master the non-volatile ultra-fast material switching. This will be made through fundamental studies of different volume-changing (nano-)materials exhibiting isostructural transformations. These studies will be carried out by a new task force built on complementary expertise in the fields of photo-induced phase transitions (Rennes), picosecond (non-linear) acoustics (Le Mans), and correlated electrons materials (Nantes). All these assets lay solid foundations for achieving the goal in ELASTICA, built around two research objectives:
1) Watching and controlling the impact of light-induced elastic cooperativity;
2) Routing of bi-stable materials from volatile to non-volatile photo-switch.