Micrometer x-ray diffraction study of VO2 films:: Separation between metal-insulator transition and structural phase transition

In order to clarify whether VO2 is a Mott insulator or a Peierls insulator, the metal-insulator transition (MIT) and the structural phase transition (SPT) are simultaneously monitored for VO2 films by current-voltage curve and diffraction measurements using a synchrotron micro-x-ray beam. In the regime showing a metallic conductivity below the SPT temperature (approximately 70 degrees C), only the diffraction planes of the monoclinic structure are observed, while planes of the tetragonal structure are absent. This observation reveals the presence of a monoclinic and metal phase between the MIT and the SPT as a characteristic of a Mott insulator.