65 research outputs found

    Superconductivity in the α-Form Layer Structured Metal Nitride Halide

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    Layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) have two polymorphs, including α- and β-forms, which have the FeOCl and SmSI structures, respectively. These compounds are band insulators and become metals and show superconductivity after electron doping by intercalating alkali metals between the layers. The superconductivity of β-form had been extensively characterized from decades ago, but it is not easy to consistently interpret all experimental results using conventional phonon-mediated Bardeen–Cooper–Schriefer mechanisms. The titanium compound TiNCl crystallizes only in the α-form structure. TiNCl also exhibits superconductivity as high as ~16 K after electron doping by intercalating metals and/or organic basis. It is important to compare the superconductivity of different M–N networks. However, α-form compounds are vulnerable to moisture, unlike β-form ones. The intercalation compounds are even more sensitive to humid air. Thus, there are few experimental studies on the superconducting mechanism of α-form, although it has been discussed for exotic Cooper-pairing mechanisms. This short review gathers the recent progress in experimental studies of TiNCl

    Angle-resolved photoemission study of Si electronic structure: Boron concentration dependence

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    The boron concentration dependence of the Si electronic structure of Si(100)2 × 1 surfaces were investigated by angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra exhibit rigid shifts toward lower binding energy as the boron concentration increases. The band dispersion was obtained from fitting procedure, and it is found that the top of the valence band does not exceed the Fermi level even with a boron concentration 35 times larger than the critical concentration of the metal-insulator transition

    Advances in Superconductivity as a road to meet Energy and Health SDGs: joint Japanese and European research teams may take the lead

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    Based on a statistical analysis of R&D activities in the field of superconductivity (SC) in a broad sense, the paper reports that Japan's leadership is strong over the past 20 years, in terms of researchers publications and patents. It also essentially shows that among the main world players, the Japanese normalized contribution is significantly dominating, although some trend towards a diminished leadership is observed in the data over the period 2005 -present time. Finally, the paper highlights that by taking advantage of their internationally recognized expertise in the field, joint Japanese and European research teams may advance superconductivity as a reliable road to meet Energy and Health SDGs (Sustainable Development Goals -UNESCO 2015)

    Soft x-ray irradiation induced metallization of layered TiNCl

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    We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (EF) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p–3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl
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