A role of a picosecond strain in an ultrafast optically-driven phase transition in VO2 nanostructures

We report on experimental picosecond acoustic studies of an ultrafast photoinduced insulator-to-metal and structural transition in VO₂ nanostructures epitaxially grown on Al₂O₃ substrates with different orientations. Applying a pump-probe technique with combined excitation of a sample with picosecond strain and femtosecond laser pulses we demonstrate that dynamical strain of moderate amplitude of 0.1% has a pronounced impact on ultrafast photoinduced phase transition in VO₂ nanohillocks. This enables novel path for controlling such transitions at picosecond and nanometer scales. Our experiments also allowed characterizing elastic and photo-elastic properties of the photo-induced metallic phase in VO₂ and to relate them to the properties of the equilibrium phase. Furthermore, we demonstrate the generation of picosecond strain pulses upon laser-induced excitation of thin epitaxial VO₂.