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arXiv · 1408.3209

Instantaneous band gap collapse in photoexcited monoclinic VO$_2$ due to photocarrier doping

Daniel Wegkamp·Marc Herzog·Lede Xian·Matteo Gatti·Pierluigi Cudazzo·Christina L. McGahan·Robert E. Marvel·Richard F. Haglund Jr.·Angel Rubio·Martin Wolf·Julia Stähler
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Abstract

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.

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Daniel Wegkamp, Marc Herzog, Lede Xian, Matteo Gatti, Pierluigi Cudazzo, Christina L. McGahan, Robert E. Marvel, Richard F. Haglund Jr., Angel Rubio, Martin Wolf, Julia Stähler. 2014-10-10. Instantaneous band gap collapse in photoexcited monoclinic VO$_2$ due to photocarrier doping. https://doi.org/10.1103/physrevlett.113.216401

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