Phase transition dynamics in high-pressure VO$_{2}$

Vanadium dioxide VO$_{2}$ is a prototypical strongly correlated material which presents an insulator-metal transition at both ambient and high pressures. We use synchrotron X-ray diffraction combined with a diamond anvil cell to determine the pressure-temperature phase diagram of VO$_{2}$. We also use ultrafast coherent phonon spectroscopy to study its phase transition dynamics at high pressure. We find that, in contrast with ambient pressure experiments where strong photoexcitation promptly changes the lattice potential symmetry, at pressures as high as P$=$11 GPa the coherent phonons are still observed upon the photo-driven phase transition to the metallic state. The mechanism of the phase transition dynamics will be discussed.