Deciphering the dynamics of the light-induced phase transition in VO${}_2$

Vanadium dioxide (VO${}_2$) is central in the study of ultrafast photoinduced insulator-to-metal phase transitions in strongly correlated materials, and a primary candidate for next-generation light-driven devices. However, the physical mechanism underlying its phase transition remains unresolved. Here, we use single-cycle light transients to perform phase-resolved ultrafast spectroscopy on VO${}_2$ crystals. Our experiments reveal two processes: a structural transformation from the insulating monoclinic M1-VO${}_2$ phase to the excited metallic rutile R*-VO${}_2$ phase, followed by electron thermalization and relaxation dynamics intrinsic to the newly formed excited metallic phase.