Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping

Physical Review Letters 113, 216401 (2014)

Instantaneous band gap collapse in photoexcited monoclinic VO2 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 Stahler

Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO2 quasi-instantaneously into a metal. Therby, we exclude a Peierls mechanism and a 80 fs phonon bottleneck for the photoinduced electronic transition of VO2. Firstprinciples many-body perturbation theory calculations reveal a high sensitivity of the VO2 band gap 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 originates from carrier photoexcitation from localised V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occured.

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We gratefully acknowledge intense and fruitful discussions with S.Wall and A. Leitenstorfer as well as the very useful comments from L. Perfetti with regard to sample preparation. REM, CLM and RFH were supported by the National Science Foundation (DMR-1207507). AR, PC and LX acknowledge support by the European Research Council Advanced Grant DYNamo (ERC-2010- AdG-267374) and Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-578-13). AR, PC, LX, MW and JS received support from the European Commission project CRONOS (Grant number 280879-2) and MG from a Marie Curie FP7 Integration Grant within the 7th European Union Framework Programme. Computational time was granted by GENCI (Project No. 544) and BSC “Red Espanola de Supercomputacion”. DW acknowledges support from the Leibniz Graduate School DinL.

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