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Sci Rep. 2020 Jan 30;10(1):1541. doi: 10.1038/s41598-020-58057-9.

Thickness-induced metal to insulator transition in Ru nanosheets probed by photoemission spectroscopy: Effects of disorder and Coulomb interaction.

Author information

1
Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan. ootsuki.daiki.4z@kyoto-u.ac.jp.
2
Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan.
3
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-hiroshima, 739-0046, Japan.
4
Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan.
5
SPring-8/JASRI, 1-1-1 Koto, Sayo-cho, Hyogo, 679-5198, Japan.
6
Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan.
7
Office of Society-Academia Collaboration for Innovation, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan.
8
Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan. yoshida.teppei.8v@kyoto-u.ac.jp.

Abstract

We investigated the electronic structures of mono- and few-layered Ru nanosheets (N layers (L) with N = 1, ~6, and ~9) on Si substrate by ultra-violet and x-ray photoemission spectroscopies. The spectral density of states (DOS) near EF of ~6 L and 1 L is suppressed as it approaches EF in contrast to that of ~9 L, which is consistent with the Ru 3 d core-level shift indicating the reduction of the metallic conductivity. A power law g(ε) ∝ |ε - εF|α well reproduces the observed spectral DOS of ~6 L and 1 L. The evolution of the power factor α suggests that the transition from the metallic state of ~9 L to the 2-dimensional insulating state with the soft Coulomb gap of 1 L through the disordered 3-dimensional metallic state of ~6 L.

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