6 February 2009 Photo-induced insulator-metal phase transition observed by the terahertz pump-probe spectroscopy
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We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation at 800 nm induced an ultrafast decrease of the transmittance of the terahertz pulse within 0.7 ps, and then the transmittance decreases gradually up to 100 ps. The decrease of the transmittance is assigned to the appearance of the high electric conductivity due to metallic state. The conductivity increases more than ten times in the picoseconds time range after photoexcitation and it is concluded that the metallic electronic states appear. The rapid and gradual changes of the electric conductivity are very similar to the previous reports of the time resolved X-ray and electron diffractions. This fact indicates that the increase of the electric conductivity and the change of the lattice structure proceed in parallel. It is suggested that the photo-induced insulator-metal phase transition is of the Peierls type.
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Makoto Nakajima, Makoto Nakajima, Naoko Takubo, Naoko Takubo, Zenji Hiroi, Zenji Hiroi, Yutaka Ueda, Yutaka Ueda, Tohru Suemoto, Tohru Suemoto, "Photo-induced insulator-metal phase transition observed by the terahertz pump-probe spectroscopy", Proc. SPIE 7214, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIII, 72140Q (6 February 2009); doi: 10.1117/12.810003; https://doi.org/10.1117/12.810003

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