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

Daiki Ootsuki,Hirofumi Namatame,Kenjiro Kodera,Masahito Morita,Hiroshi Kumigashira,Akira Yasui,Koji Horiba,Masaki Taniguchi,Satoshi Toyoda,Katsutoshi Fukuda,Teppei Yoshida,Daiya Shimonaka,Yoshiharu Uchimoto,Eiji Ikenaga,Makoto Minohara,Masashi Arita

doi:10.1038/s41598-020-58057-9

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.

Highlights

IntroductionWe investigated how the electronic structure evolves from the mono- (1 L) to few layered Ru nanosheets ~6 and ~9 L on Si substrate by performing photoemission spectroscopy in order to clarify the mechanism of the disappearance of the metallic conductivity
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
We investigated how the electronic structure evolves from the mono- (1 L) to few layered Ru nanosheets ~6 and ~9 L on Si substrate by performing photoemission spectroscopy in order to clarify the mechanism of the disappearance of the metallic conductivity

Summary

Introduction

We investigated how the electronic structure evolves from the mono- (1 L) to few layered Ru nanosheets ~6 and ~9 L on Si substrate by performing photoemission spectroscopy in order to clarify the mechanism of the disappearance of the metallic conductivity. We observed the chemical shifts of Ru 3 d core-level spectra and the suppression of the spectral weight at Fermi-level (EF) with decreasing the number of stacking layers. These indicate the disappearance of the metallic conductivity in the mono-layered Ru nanosheets. 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

Methods

Results

Conclusion