Transient dynamics of the phase transition in VO2 revealed by mega electron-volt ultrafast electron diffraction

Abstract

Vanadium dioxide (VO2) exhibits an insulator-to-metal transition accompanied by a structural transition near room temperature. This transition can be triggered by an ultrafast laser pulse. Exotic transient states, such as a metallic state without structural transition, were also proposed. These unique characteristics let VO2 have great potential in thermal switchable devices and photonic applications. Although great efforts have been made, the atomic pathway during the photoinduced phase transition is still not clear. Here, we synthesized freestanding quasi-single-crystal VO2 films and examined their photoinduced structural phase transition with mega-electron-volt ultrafast electron diffraction. Leveraging the high signal-to-noise ratio and high temporal resolution, we observe that the disappearance of vanadium dimers and zigzag chains does not coincide with the transformation of crystal symmetry. After photoexcitation, the initial structure is strongly modified within 200 femtoseconds, resulting in a transient monoclinic structure without vanadium dimers and zigzag chains. Then, it continues to evolve to the final tetragonal structure in approximately 5 picoseconds. In addition, only one laser fluence threshold instead of two thresholds suggested in polycrystalline samples was observed in our quasi-single-crystal samples. Our findings provide new essential information for a comprehensive understanding of the photoinduced ultrafast phase transition in VO2.

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Cited by in corpus (8)

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• Decoupled few-femtosecond phase transitions in vanadium dioxide
• Imaging the photochemical dynamics of cyclobutanone with MeV ultrafast electron diffraction
• Nature of the photo-induced metallic state in monoclinic VO${}_2$
• Megahertz cycling of ultrafast structural dynamics enabled by nanosecond thermal dissipation
• Light-induced phase transitions in vanadium dioxide: a tensor network study
• Poincaré sphere engineering of dynamical ferroelectric topological solitons
• Small polarons mediated near-room-temperature metal-insulator transition in vanadium dioxide and their hopping dynamics