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Sci Rep. 2017 Nov 22;7(1):16038. doi: 10.1038/s41598-017-16188-6.

Mott transition in chain structure of strained VO2 films revealed by coherent phonons.

Author information

1
Metal-Insulator-Transition Laboratory, Electronics and Telecommunications Research Institute, Daejeon, 34129, Republic of Korea.
2
Department of Advanced Device Technology, University of Science and Technology, Daejeon, 34129, Republic of Korea.
3
Department of Physics, Chungnam National University, Daejeon, 34134, South Korea.
4
Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS, Université de Strasbourg, 67034, Strasbourg, Cedex 02, France.
5
Center for Electron Microscopy Research, Korea Basic Science Institute, Daejeon, 34133, Republic of Korea.
6
Metal-Insulator-Transition Laboratory, Electronics and Telecommunications Research Institute, Daejeon, 34129, Republic of Korea. htkim@etri.re.kr.
7
Department of Advanced Device Technology, University of Science and Technology, Daejeon, 34129, Republic of Korea. htkim@etri.re.kr.

Abstract

The characteristic of strongly correlated materials is the Mott transition between metal and insulator (MIT or IMT) in the same crystalline structure, indicating the presence of a gap formed by the Coulomb interaction between carriers. The physics of the transition needs to be revealed. Using VO2, as a model material, we observe the emergence of a metallic chain in the intermediate insulating monoclinic structure (M2 phase) of epitaxial strained films, proving the Mott transition involving the breakdown of the critical Coulomb interaction. It is revealed by measuring the temperature dynamics of coherent optical phonons with separated vibrational modes originated from two substructures in M2: one is the charge-density-wave, formed by electron-phonon (e-ph) interaction, and the other is the equally spaced insulator-chain with electron-electron (e-e) correlations.

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