Ultrafast photoinduced transition of an insulating VO2 thin film into a nonrutile metallic state

Rikiya Yoshida, Takashi Yamamoto, Yukiaki Ishida, Hiroki Nagao, Tsubasa Otsuka, Kuninari Saeki, Yuji Muraoka, Ritsuko Eguchi, Kyoko Ishizaka, Takayuki Kiss, Shuntaro Watanabe, Teruto Kanai, Jiro Itatani, Shik Shin

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Using time-resolved photoemission spectroscopy, we have investigated the nonequilibrium electronic structures of a VO2 thin film upon photoexcitation. We employed the high-harmonic generation method, which was crucial in obtaining the results. Irradiation by a 170-fs optical pulse at a fluence above ∼6 mJ/cm2 rapidly converts the insulating VO2 thin film into a metallic state, and we show that the transition is accompanied by a spectral-weight redistribution over a 1-eV scale. This observation provides direct spectroscopic evidence of an ultrafast insulator-to-metal transition. The transient metallic state has a unique spectrum that deviates from the static spectrum of the rutile metal phase. We also observe an anomalous spreading of spectral weight up to ∼0.4 eV above the Fermi level as soon as the transient metallic state emerges. The temporal evolution of the spectral weight near the Fermi level exhibits an ultrafast increase and a subsequent slower increase over ∼3 ps. We suggest that a broadening mechanism related to the excitation of phonon modes is responsible for the spreading of the spectral weight and that the slower increase of the spectral weight is associated with the expansion of the metallic region after photoinduced nucleation. In addition, the initial nucleation of the metallic state appears to be spatially inhomogeneous even near the surface. The results of this study highlight the uniqueness of the nonequilibrium metallic state in comparison to the equilibrium rutile metallic state from an electronic-state perspective.

Original languageEnglish
Article number205114
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume89
Issue number20
DOIs
Publication statusPublished - May 15 2014

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Fermi level
Nucleation
Thin films
Photoexcitation
Electronic states
Photoelectron spectroscopy
Harmonic generation
thin films
Electronic structure
Transition metals
Laser pulses
rutile
Metals
Irradiation
nucleation
uniqueness
photoexcitation
harmonic generations
fluence
photoelectric emission

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

Ultrafast photoinduced transition of an insulating VO2 thin film into a nonrutile metallic state. / Yoshida, Rikiya; Yamamoto, Takashi; Ishida, Yukiaki; Nagao, Hiroki; Otsuka, Tsubasa; Saeki, Kuninari; Muraoka, Yuji; Eguchi, Ritsuko; Ishizaka, Kyoko; Kiss, Takayuki; Watanabe, Shuntaro; Kanai, Teruto; Itatani, Jiro; Shin, Shik.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 89, No. 20, 205114, 15.05.2014.

Research output: Contribution to journalArticle

Yoshida, R, Yamamoto, T, Ishida, Y, Nagao, H, Otsuka, T, Saeki, K, Muraoka, Y, Eguchi, R, Ishizaka, K, Kiss, T, Watanabe, S, Kanai, T, Itatani, J & Shin, S 2014, 'Ultrafast photoinduced transition of an insulating VO2 thin film into a nonrutile metallic state', Physical Review B - Condensed Matter and Materials Physics, vol. 89, no. 20, 205114. https://doi.org/10.1103/PhysRevB.89.205114
Yoshida, Rikiya ; Yamamoto, Takashi ; Ishida, Yukiaki ; Nagao, Hiroki ; Otsuka, Tsubasa ; Saeki, Kuninari ; Muraoka, Yuji ; Eguchi, Ritsuko ; Ishizaka, Kyoko ; Kiss, Takayuki ; Watanabe, Shuntaro ; Kanai, Teruto ; Itatani, Jiro ; Shin, Shik. / Ultrafast photoinduced transition of an insulating VO2 thin film into a nonrutile metallic state. In: Physical Review B - Condensed Matter and Materials Physics. 2014 ; Vol. 89, No. 20.
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