%0 Journal Article
%T Instantaneous band gap collapse in photoexcited monoclinic VO$_2$ due to photocarrier doping
%A Daniel Wegkamp
%A Marc Herzog
%A Lede Xian
%A Matteo Gatti
%A Pierluigi Cudazzo
%A Christina L. McGahan
%A Robert E. Marvel
%A Richard F. Haglund Jr.
%A Angel Rubio
%A Martin Wolf
%A Julia St£¿hler
%J Physics
%D 2014
%I arXiv
%R 10.1103/PhysRevLett.113.216401
%X Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO$_2$ quasi-instantaneously into a metal. Thereby, we exclude an 80 femtosecond structural bottleneck for the photoinduced electronic phase transition of VO$_2$. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO$_2$ bandgap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructral 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 \emph{before} significant hot-carrier relaxation or ionic motion has occurred.
%U http://arxiv.org/abs/1408.3209v2