Ultrafast control of quantum materials: the non-thermal dynamical strain pathway – FASTRAIN

Driving matter far away from equilibrium by ultrafast laser pulse opens new avenues to direct materials to other macroscopic phases through non-thermal dynamical pathways. The FASTRAIN project aims to unravel the physical backgrounds of ultrafast phase transitions in quantum materials caused by a universal non-thermal mechanism, whereby dynamic strain waves are directly photoinduced in the material and trigger a phase transformation. This uncharted mechanism is however potentially present in any photoinduced transitions involving volume and/or ferroelastic deformation. Photoexcitation by an ultrafast laser indeed generates an elastic stress, which will be relaxed by launching a volume (and/or symmetry change) strain wave. In this project, we will focus on Mott insulators, a large class of correlated quantum materials widely studied since half a century. We plan to demonstrate and rationalize the crucial role of the strain wave mechanisms on the photoinduced Mott insulator to metal transitions, which are inherently coupled to a volume change. Our time-resolved preliminary results probing electronic (reflectivity) and structural (X-ray diffraction) properties have established that a laser pulse drives the Mott insulator V2O3 towards a complete insulator-metal transition controlled by a strain wave. In this project, we will clarify the respective impact of symmetry breaking and volume change on the multiscale dynamics along the photoinduced transition pathway. Moreover, we will explore the link between local precursors and macroscopic phase transformation. Finally, we will clarify the conditions favoring the insulator-to-metal conversion, which can be complete in granular thin films and limited in bulk crystals. The FASTRAIN project brings together a wide range of expertise ranging from correlated quantum materials (IMN, GREMAN) to the physics of photoinduced phase transitions (IPR, ESRF). The ideas developed in FASTRAIN will impact other fields, especially the broad class of quantum materials presenting a phase transition involving elastic deformations. It will also shed light on our understanding and assess the ultimate performance of future innovative devices, such as hardware neural networks for artificial intelligence based on Mott insulators.