Spin-Polarized Positronium Time-of-Flight Spectroscopy for Probing Spin-Polarized Surface Electronic States

M. Maekawa, A. Miyashita, S. Sakai, S. Li, S. Entani, A. Kawasuso, and Y. Sakuraba
Phys. Rev. Lett. 126, 186401 – Published 4 May 2021

Abstract

The energy spectrum of positronium atoms generated at a solid surface reflects the electron density of states (DOS) associated solely with the first surface layer. Using spin-polarized positrons, the spin-dependent surface DOS can be studied. For this purpose, we have developed a spin-polarized positronium time-of-flight spectroscopy apparatus based on a Na22 positron source and an electrostatic beam transportation system, which enables the sampling of topmost surface electrons around the Γ point and near the Fermi level. We applied this technique to nonmagnetic Pt(111) and W(001), ferromagnetic Ni(111), Co(0001) and graphene on them, Co2FeGa0.5Ge0.5 (CFGG) and Co2MnSi (CMS). The results showed that the electrons of Ni(111) and Co(0001) surfaces have characteristic negative spin polarizations, while these spin polarizations vanished upon graphene deposition, suggesting that the spin polarizations of graphene on Ni(111) and Co(0001) were mainly induced at the Dirac points that were out of range in the present measurement. The CFGG and CMS surfaces also exhibited only weak spin polarizations suggesting that the half-metallicity expected for these bulk states was not maintained at the surfaces.

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  • Received 5 November 2020
  • Accepted 25 March 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.186401

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Maekawa, A. Miyashita, S. Sakai, S. Li, S. Entani, and A. Kawasuso*

  • National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan

Y. Sakuraba

  • National Institute for Materials Science (NIMS), 1-2-1, Sengen, Tsukuba-city, Ibaraki 305-0047, Japan

  • *Corresponding author. kawasuso.atsuo@qst.go.jp

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Vol. 126, Iss. 18 — 7 May 2021

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