Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic ${\mathrm{VO}}_2$ quasi-instantaneously into a metal. Thereby, we exclude an 80 fs structural bottleneck for the photoinduced electronic phase transition of ${\mathrm{VO}}_2$. First-principles many-body perturbation theory calculations reveal a high sensitivity of the ${\mathrm{VO}}_2$ band gap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructural insulator-to-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V $3d$ valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

• Received 15 July 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.216401