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• 機械学習で新しい超伝導物質を探索する:21世紀版マティアス則への期待

  松本 要, 堀出 朋哉

  応用物理  ( 公益社団法人 応用物理学会 )  89 ( 4 ) 222 - 226   2020年01月  [査読有り]  [招待有り]

   概要を見る

  <p>初期の超伝導物質探索においてマティアス則が活躍した．マティアス則とは，遷移金属およびその合金の臨界温度<i>T</i>_cがある特定の物質パラメータの組み合わせにおいて極大になるという経験則で，多くの超伝導物質の発見につながった．ところが最近，計算機パワーの進展に伴い，全く新しい経験的な<i>T</i>_c予測法が生みだされる可能性がある．それは最新の超伝導データベースと人工知能技術の一種である機械学習を用いて，計算機に既知物質の<i>T</i>_c実験値とその元素の組み合わせを学習させ，得られた学習モデルを未知物質の元素の組み合わせに適用して<i>T</i>_cを予測する手法である．これは強いていえば，21世紀版のマティアス則と呼ばれるようなもので，本稿は，この新しい超伝導物質探索手法に関するものである．</p>

  DOI CiNii

• Deposition-Temperature Dependence of Vortex Pinning Property in YBa₂Cu₃O₇+BaHfO₃ Films

  Horide Tomoya, Torigoe Kenta, Kita Ryusuke, Nakamura Ryota, Ishimaru Manabu, Awaji Satoshi, Matsumoto Kaname

  MATERIALS TRANSACTIONS  ( 公益社団法人 日本金属学会 )  61 ( 3 ) 449 - 454   2020年01月  [査読有り]

   概要を見る

  <p>Improvement of critical current density (<i>J</i>_c) in magnetic fields is required in YBa₂Cu₃O₇ films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa₂Cu₃O₇+BaHfO₃ films to control the nanorod structure, and its influence on <i>J</i>_c was analyzed. The YBa₂Cu₃O₇+BaHfO₃ film deposited at 850°C exhibited pinning force maximum (<i>F</i>_p,max) as high as 413 GN/m³ at 40 K, while the <i>F</i>_p,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa₂Cu₃O₇+BaHfO₃ film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the <i>F</i>_p,max in high temperatures, since the critical temperature and matching field dependences of <i>J</i>_c value dominate the <i>F</i>_p,max. On the other hand, low deposition temperature improves the <i>F</i>_p,max in low temperatures since the <i>F</i>_p shift in accordance with matching field is dominant to the <i>F</i>_p,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa₂Cu₃O₇ films containing nanorods considering the <i>J</i>_c variation with critical temperature and matching field.</p><p> </p><p>This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. <b>83</b> (2019) 320–326.</p>

  DOI CiNii

• Thermoelectric Property in Orthorhombic-Domained SnSe Film

  Horide T., Murakami Y., Hirayama Y., Ishimaru M., Matsumoto K.

  ACS Applied Materials and Interfaces    11 ( 30 ) 27057 - 27063   2019年07月  [査読有り]

   概要を見る

  © 2019 American Chemical Society. Single-crystal SnSe exhibits extremely high thermoelectric properties, and fabrication of SnSe films is promising for practical application and basic research on properties. However, the high thermoelectric properties have not yet been reported in SnSe films and their thermoelectric properties and nanostructure have not yet been analyzed in detail. In the present study, a-axis-oriented epitaxial SnSe films were prepared to discuss the thermoelectric properties of the SnSe films. While the electrical conductivity of the films was orders of magnitude smaller than that in the single crystals at room temperature, surprisingly, the thermoelectric property (power factor) of the films was slightly higher than that in the single crystals at high temperatures (∼300 °C). The SnSe films contained orthorhombic domain boundaries with a spacing of several hundred nanometers. The orthorhombic domain boundaries caused carrier scattering and degraded the mobility of the films at room temperature, but their effect decreased with increasing temperature. Thus, the carrier scattering at domain boundaries results in characteristic temperature dependence of thermoelectric properties in the SnSe films. High thermoelectric properties at high temperatures were successfully achieved in the SnSe films in spite of the existence of domain boundaries, demonstrating the possibility of high-performance of SnSe thermoelectric films.

  DOI Scopus

• Observation of inhomogeneous depinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf> composite multilayers

  Horide T., Ishimaru M., Matsumoto K.

  Superconductor Science and Technology    32 ( 8 )   2019年06月  [査読有り]

   概要を見る

  © 2019 IOP Publishing Ltd. Composite multilayer films (CMLs) comprising YBa2Cu3O7 + BaHfO3 (4.7 vol%)/YBa2Cu3O7 + BaHfO3 (3.1 vol%) were fabricated, and vortex behavior in the CMLs was evaluated to discuss inhomogeneous depinning of vortices. Magnetic field and angular dependences of critical current density (J c) in the CMLs were similar to those in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) single layer film (SL). Variation of the CML structure shifted the matching field effect in global pinning force and irreversibility temperature. The J c in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) SL was smaller than that in the YBa2Cu3O7 + BaHfO3 (3.1 vol%) SL, suggesting that vortices preferentially moved along the low-J c layers in the CMLs. The high-J c layers pinned the vortices in the low-J c layers, resulting in a shift of the matching field effect. These observations are characteristic of inhomogeneous depinning of vortices in the CMLs. The inhomogeneous depinning as well as pinned configuration should be considered for understanding J c and for structural design of pinning centers in YBa2Cu3O7 films.

  DOI Scopus

• Nonlocal self-organization of long stacking faults from highly strained nanocomposite film of complex oxide

  Horide T., Ishimaru M., Sato K., Matsumoto K.

  Physical Review Materials    3 ( 1 )   2019年01月  [査読有り]

   概要を見る

  © 2019 American Physical Society. Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5-30 nm and a length of >500nm were self-organized by ex situ annealing highly strained nanocomposite films of YBa2Cu3O7-δ(YBCO)+BaMO3(M=Hf,Sn). It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over >500nm, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure YBCO film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations.

  DOI Scopus

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• 量子化磁束のダイナミクス制御と物質科学への展開

  基盤研究(S)

  研究期間:  2011年05月  -  2016年03月

  研究課題番号:  23226014

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• エネルギーを操る革新的なマテリアルたち－太陽電池，超伝導，革新的エネルギー・マテリアルー

  2014年07月

  　

  　

   概要を見る

  筑紫女学園高等学校

• 材料の元になる元素はどこからやってきたの？宇宙・星の一生から地球へ　―元素の旅―

  2014年03月

  　

  　

   概要を見る

  明治学園中学高校

• エネルギーを操る革新的なマテリアルたち－太陽電池，超伝導，革新的エネルギー・マテリアルー

  2014年01月

  　

  　

   概要を見る

  福岡県立八幡高等学校

• 材料の元になる元素はどこからやってきたの？宇宙・星の一生から地球へ　―元素の旅―

  2013年08月

  　

  　

   概要を見る

  鹿児島県立鹿児島中央高等学校