Propagation of insulator-to-metal transition driven by photoinduced strain waves in a Mott material

Ultrafast photoexcitation can generate internal compressive stress in Mott insulators that lead to strain waves from free surfaces. These photoinduced elastic waves can trigger phase transitions in materials. However, a comprehensive physical picture of the phase transformation dynamics that includes acoustic-scale propagation has not yet been developed. Here we demonstrate that such a strain-wave mechanism drives the ultrafast insulator-to-metal phase transition in granular thin films of the Mott material V2O3. Our time-resolved optical reflectivity and X-ray diffraction measurements reveal that an inverse ferroelastic shear occurs before the insulator-to-metal transition, which propagates in the wake of a compressive strain wave. These dynamics are governed by the domain size and film thickness, respectively. Our results clarify the morphological conditions for the ultrafast phase transition that is favoured in granular thin films and hindered in single crystals. The resulting physical picture sheds light on the ultrafast phase transitions in quantum materials and future devices based on Mott insulators. The mechanism behind the ultrafast insulator-to-metal transition in Mott materials is still not well understood. Now, it is shown that this phase transition propagates along the pathway of a photoinduced compressive strain wave in prototypical V2O3.