Observation of instabilities in metallic states for metal-to-insulator switch oxides

Vanadium dioxide (VO2) shows a metal-to-insulator (MI) switch near room temperature (Fig. 1). Since switching phenomena near room temperature are rare, VO2 has attracted attention for its switching mechanism, namely, the instability in the metallic state. Theoretical work on electronic structures of VO2 40 years ago suggested that the instability is responsible for electron-phonon interaction [1]. Since then, much interest has been directed to experimental studies of electronic structures of VO2 using angle-resolved photoemission electron spectroscopy (ARPES).

However, ARPES measurements of VO2 single crystals are difficult to perform because of the difficulty in obtaining a chemically stable cleavage plane in VO2 single crystals with three-dimensional crystal structure.

Now, Yuji Muraoka and colleagues at Okayama University, High Energy Accelerator Research Organization, and University of Tokyo have determined the electronic structures of the metallic phase of VO2 through studies of VO2 epitaxial thin films grown on TiO2(001) substrates, using synchrotron radiation ARPES.

The electronic structures possessed a flat portion that is evidence for the presence of electron-phonon interaction predicted by theoretical work (Fig. 2).

The results obtained by Muraoka and colleagues strongly indicate the importance of electron-phonon interaction for the origin of the instability in the metallic state of VO2, and support the validity of theoretical work.

This research advances the understanding of the mechanism for the MI switch in VO2, and provides fundamental knowledge for controlling the switching temperature for potential applications.

[1] M. Gupta, A. J. Freeman, and D. E. Ellis, Phys. Rev. B 16, 3338 (1977).

Reference:

• Authors: Yuji Muraoka1, Hiroki Nagao2, Yuichiro Yao2, Takanori Wakita1, Kensei Terashima1, Takayoshi Yokoya1, Hiroshi Kumigashira3,*, and Masaharu Oshima4.
• Title of original paper: Fermi surface topology in a metallic phase of VO2 thin films grown on TiO2(001) substrates.
• Journal, volume, pages and year: Scientific Reports 8, 17906 (2018).
• Digital Object Identifier (DOI): 10.1038/s41598-018-36281-8
• Journal website: https://www.nature.com/articles/s41598-018-36281-8
• Affiliations: 1Research Institute for Interdisciplinary Science, Okayama University, 2Graduate School of Natural Science and Technology, Okayama University, 3High Energy Accelerator Research Organization (KEK), Photon Factory, 4The Institute for Solid State Physics, The University of Tokyo.
• *Present address: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
• Department website:http://www.science.okayama-u.ac.jp/~surface/index.html
• Okayama University Scientific Achievement Repository: http://ousar.lib.okayama-u.ac.jp/57013