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Surface valence transition in SmS by alkali metal adsorption

Takuto Nakamura1,2,*, Toru Nakaya2, Yoshiyuki Ohtsubo3,1,2, Hiroki Sugihara2, Kiyohisa Tanaka4, Ryu Yukawa5, Miho Kitamura6, Hiroshi Kumigashira7, Keiichiro Imura8,† et al.

Hiroyuki S. Suzuki9, Noriaki K. Sato8,10, and Shin-ichi Kimura1,2,4,‡

  • 1Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
  • 2Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
  • 3National Institutes for Quantum Science and Technology, Sendai 980-8579, Japan
  • 4Institute for Molecular Science, Okazaki 444-8585, Japan
  • 5Graduate School of Engineering, Osaka University, Suita 565-0871, Japan
  • 6Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba 305-0801, Japan
  • 7Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai 980-8577, Japan
  • 8Department of Physics, Nagoya University, Nagoya 464-8602, Japan
  • 9Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
  • 10Center for General Education, Aichi Institute of Technology, Toyota 470-0392, Japan

  • *nakamura.takuto.fbs@osaka-u.ac.jp
  • †Present address: National Institutes for Institute of Liberal Arts and Sciences, Nagoya University, Nagoya 464-8601, Japan.
  • ‡kimura.shin-ichi.fbs@osaka-u.ac.jp
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Phys. Rev. B 107, L041102 – Published 5 January, 2023

DOI: https://doi.org/10.1103/PhysRevB.107.L041102

Abstract

The electronic structure changes of SmS surfaces under potassium (K) doping are elucidated using synchrotron-based core-level photoelectron spectroscopy and angle-resolved photoelectron spectroscopy (ARPES). The Sm core-level and ARPES spectra indicate that the Sm mean valence of the surface increased from the nearly divalent to trivalent states, with increasing K deposition. Carrier-induced valence transition (CIVT) from Sm2+ to Sm3+ exhibits a behavior opposite to that under conventional electron doping. Excess electrons from K atoms are transferred to S sites and the liberated electrons from Sm3+ ions due to CIVT at the surface are trapped like local excitons around the Sm3+ ions, which is inconsistent with the phase transition from the black insulator with Sm2+ to the gold metal with Sm3+ under pressure. This CIVT helps to clarify the pressure-induced black-to-golden phase transition in this material, which originates from the Mott transition of excitons.

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Phys. Rev. B 107, L041102– Published 5 January, 2023
  • Received 30 May 2022
  • Revised 13 December 2022
  • Accepted 14 December 2022
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