Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Volume 76 , Issue 11
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Recollections: Special Episodes “Commemorating Prof. Koshiba”
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  • Takayuki Tachibana, Yasuyuki Nagashima
    Type: Researches
    2021 Volume 76 Issue 11 Pages 723-728
    Published: November 05, 2021
    Released: November 05, 2021

    We compared positron and electron-stimulated desorption (e+SD and ESD) of positive ions from a TiO2(110) surface. Although desorption of O+ ions was observed in both experiments, the yield of e+SD was one order of magnitude higher than the yield of ESD at an incident energy of 500 eV. Furthermore, e+SD of O+ ions caused even below the ESD threshold and remained highly efficient with incident positron energies between 10 eV and 600 eV. The results indicate that e+SD of O+ ions is predominantly caused by pair annihilation of surface-trapped positrons with inner-shell electrons. We also observed the ion desorption from water chemisorbed on the TiO2 surface and found that the desorption of specific ions was enhanced in e+SD. This finding corroborates our conclusion that annihilation-site selectivity of positrons results in site-selective ion desorption.

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  • Hideaki Sakai
    Type: Researches
    2021 Volume 76 Issue 11 Pages 729-734
    Published: November 05, 2021
    Released: November 05, 2021

    Recently, the coupling of Dirac/Weyl fermions with quantum phenomena in solids, such as magnetism, has been intensively investigated, since unconventional transport and optical phenomena were revealed. However, the material variety of the correlated topological materials has been still limited. Here we propose that layered material AMn X2( A: alkaline and rare earth ions, X: Sb, Bi) is a promising platform for this. AMn X2 consists of the alternative stack of the X square net layer hosting quasi 2D Dirac fermions and the A2+–Mn2+X 3-magnetic block layer. By systematically substituting the A and X sites, we have demonstrated that the Dirac fermion state in the former layer can be controlled and even enriched by the coupling with the physical properties of the block layer.

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