Propagating insulator-to-metal transition in the wake of photoinduced strain waves in a Mott material

Ultrafast physics opens new avenues for directing materials to different functional macroscopic states on non-thermal dynamical pathways. In any phase transition involving volume and/or ferroelastic deformation, an often overlooked mechanism emerges whereby photoinduced elastic waves drive the transition. However, a comprehensive physical picture of transformation dynamics which includes acoustic scale propagation remained elusive. Here we show that such strain wave mechanism drives the ultrafast insulator-to-metal phase transition (IMT) in the V₂O₃ Mott material. We discuss the underlying physics based on time-resolved optical reflectivity and X-ray diffraction probing granular thin films. We evidence the role of strain wave mechanisms in ultrafast changes either with or without symmetry breaking. We reveal inverse ferroelastic shear occurring before the IMT propagating in the wake of compressive strain wave. These dynamics are shown to be governed by the domain size and the film thickness, respectively. A fluence threshold is evidenced for the onset of IMT at macroscopic scale, as well as phase separation at intermediate fluence and complete transformation at saturating fluence. We clarify the morphological conditions for the ultrafast IMT that is favoured in granular thin films, and hindered in single crystals. The resulting physical picture sheds new light on the ultrafast phase transitions in quantum materials and future devices based on Mott insulators.