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Absence of ferromagnetism in MnBi$$_2$$Te$$_4$$/Bi$$_2$$Te$$_3$$ down to 6 K

深澤 拓朗*; 日下 翔太郎*; 角田 一樹; 橋爪 瑞葵*; 一ノ倉 聖*; 竹田 幸治; 出田 真一郎*; 田中 清尚*; 清水 亮太*; 一杉 太郎*; et al.

Physical Review B, 103(20), p.205405_1 - 205405_6, 2021/05

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

We successfully fabricated a MnBi$$_2$$Te$$_4$$/Bi$$_2$$Te$$_3$$ heterostructure by incorporating Mn and Te inside the topmost quintuple layer of Bi$$_2$$Te$$_3$$, as unambiguously confirmed by LEED I-V scanning transmission electron microscopy measurements. The surface-state Dirac cone of the heterostructure showed little change compared to that of the pristine Bi$$_2$$Te$$_3$$ and X-ray magnetic circular dichroism measurements showed that the system was paramagnetic down to 5.6 K. These results are in contrast to the previous works on related materials that showed magnetic order around 10 K as well as theoretical predictions and suggests the intricacy of the magnetic properties of two-dimensional van der Waals magnets.


Fabrication of a novel magnetic topological heterostructure and temperature evolution of its massive Dirac cone

平原 徹*; Otrokov, M. M.*; 佐々木 泰佑*; 角田 一樹*; 友弘 雄太*; 日下 翔太郎*; 奥山 裕磨*; 一ノ倉 聖*; 小林 正起*; 竹田 幸治; et al.

Nature Communications (Internet), 11, p.4821_1 - 4821_8, 2020/09

 被引用回数:9 パーセンタイル:90.48(Multidisciplinary Sciences)

We fabricate a novel magnetic topological heterostructure Mn$$_{4}$$Bi$$_{2}$$Te$$_{7}$$/Bi$$_{2}$$Te$$_{3}$$ where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi$$_{2}$$Te$$_{3}$$. A massive Dirac cone (DC) with a gap of 40-75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200-250 K. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi$$_{2}$$Te$$_{4}$$/Bi$$_{2}$$Te$$_{3}$$ is paramagnetic at 6 K while Mn$$_{4}$$Bi$$_{2}$$Te$$_{7}$$/Bi$$_{2}$$Te$$_{3}$$ is ferromagnetic with a negative hysteresis (critical temperature 20 K). This novel heterostructure is potentially important for future device applications.


Atomic and electronic structures of Si(111)-$$sqrt{21}timessqrt{21}$$ superstructure

深谷 有喜; 久保 敬祐*; 平原 徹*; 山崎 詩郎*; Choi, W. H.*; Yeom, H. W.*; 河裾 厚男; 長谷川 修司*; 松田 巌*

e-Journal of Surface Science and Nanotechnology (Internet), 10, p.310 - 314, 2012/07



Atomic structure of two-dimensional binary surface alloys; Si(111)-$$sqrt{21}timessqrt{21}$$ superstructure

深谷 有喜; 松田 巌*; 橋本 美絵*; 久保 敬祐*; 平原 徹*; 山崎 詩郎*; Choi, W. H.*; Yeom, H. W.*; 長谷川 修司*; 河裾 厚男; et al.

Surface Science, 606(11-12), p.919 - 923, 2012/06

 被引用回数:6 パーセンタイル:31.19(Chemistry, Physical)



Experimental investigation of bubbling in particle beds with high solid holdup

Cheng, S.*; 平原 大輔*; 田中 鷹平*; 権代 陽嗣*; Zhang, B.*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; et al.

Experimental Thermal and Fluid Science, 35(2), p.405 - 415, 2011/02

 被引用回数:23 パーセンタイル:75.32(Thermodynamics)

水を液体として用い観察タンクの底から窒素を発生させバブルを作る実験が2次元(2D)3次元(3D)それぞれの状態で個別に行われた。粒子ベッド高さ(30mmから200mm),粒子直径(0.4mmから6mm)そして、粒子タイプ(アクリルビーズ,ガラス,アルミ,ジルコニウム)等で粒子ベッドに変化を持たせた。これらの実験でイメージ解析によって初めて3種類のバブル特性が観察され、さらに表面バブル頻度、2D, 3D状態の表面バブルサイズなどのバブル挙動の定量的な詳細分析で検証された。


Experimental investigation on self-leveling behavior in debris beds

Zhang, B.*; 原田 哲志*; 平原 大輔*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; 飛田 吉春

Nuclear Engineering and Design, 241(1), p.366 - 377, 2011/01

 被引用回数:28 パーセンタイル:91.5(Nuclear Science & Technology)

In the present study, we elected to use depressurization boiling to simulate an axially increasing void distribution in the debris bed. Bottom-heating boiling was also chosen to confirm characteristics of the self-leveling process do not depend on the boiling mode. Particle size, shape, bed volume and density along with boiling intensity and total volume were taken as experimental parameters to obtain the general characteristics of the self-leveling process. Experiments with simulant materials were conducted and analyzed. The good concordance of the transient processes obtained from the different boiling methods sufficiently demonstrates the results obtained exhibit these general self-leveling characteristics. Comparisons of deduced time variations of the inclination angle provide qualitative tendencies based on the experimental parameters considered influential to self-leveling behavior. The rationale behind the definition introduced for equivalent power density is also presented.


Electron compound nature in a surface atomic layer of a two-dimensional hexagonal lattice

松田 巌*; 中村 史一*; 久保 敬祐*; 平原 徹*; 山崎 詩郎*; Choi, W. H.*; Yeom, H. W.*; 成田 尚司*; 深谷 有喜; 橋本 美絵*; et al.

Physical Review B, 82(16), p.165330_1 - 165330_6, 2010/10

 被引用回数:9 パーセンタイル:43.36(Materials Science, Multidisciplinary)

一価金属の共吸着でSi(111)表面上に形成される$$sqrt{21}timessqrt{21}$$超構造は、表面状態の電子数と吸着金属の原子数の割合が常に一定で形成される。このことは、$$sqrt{21}timessqrt{21}$$超構造が電子化合物の特性を持つことを意味している。われわれは、二次元表面合金相である$$sqrt{21}timessqrt{21}$$超構造の安定性を調べるために、Hume-Rothery型化合物における代表的な2つの理論、Jones model及びpseudopotential modelを用いて解析を行った。解析の結果、二次元表面合金相においてはJones modelが破綻しており、pseudopotential modelにおける二次元の表面状態電子を介した中距離原子間相互作用の重要性を見いだした。


Experimental study of bubble behavior in a two-dimensional particle bed with high solid holdup

Cheng, S.*; 平原 大輔*; 田中 鷹平*; 権代 陽嗣*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; 飛田 吉春

Proceedings of 18th International Conference on Nuclear Engineering (ICONE-18) (CD-ROM), 8 Pages, 2010/05



Self-leveling onset criteria in debris beds

Zhang, B.*; 原田 哲志*; 平原 大輔*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; 飛田 吉春

Journal of Nuclear Science and Technology, 47(4), p.384 - 395, 2010/04

 被引用回数:30 パーセンタイル:90.59(Nuclear Science & Technology)

We develop criteria establishing the onset of self-leveling behavior of core debris in a core-disruptive accident of a sodium-cooled fast breeder reactor. We base the criteria on a force balance model assuming a debris bed with a single-sized spherical particle. The model considers drag, buoyancy, and gravity acting on each particle. A series of experiments verified the applicability of this description of self-leveling. Particle size, shape, density, along with boiling intensity, bed volume, and even experimental methods were taken into consideration to obtain general characteristics of the self-leveling process. We used depressurization boiling to simulate an axially increasing void distribution in the debris bed. We also used bottom heating to validate the use of the depressurization method. We obtained good agreement between model predictions for the self-leveling onset and experimental results. Extrapolation of our model to actual reactor conditions is discussed.


Criteria for occurrence of self-leveling in the debris bed

Zhang, B.*; 原田 哲志*; 平原 大輔*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; 飛田 吉春

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 15 Pages, 2009/09



Experimental study of self-leveling behavior in debris bed

Zhang, B.*; 原田 哲志*; 平原 大輔*; 松元 達也*; 守田 幸路*; 福田 研二*; 山野 秀将; 鈴木 徹; 飛田 吉春

Proceedings of 6th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-6) (USB Flash Drive), 8 Pages, 2008/11



Vectorization of direct Fock matrix construction in DIRAC-DHF calculations

望月 祐志*; 松村 昌幸*; 与倉 徹一*; 平原 幸男*; 今村 俊幸

Journal of Nuclear Science and Technology, 39(2), p.195 - 199, 2002/02

 被引用回数:5 パーセンタイル:36.01(Nuclear Science & Technology)




原田 哲志*; 平原 大輔*; Zhang, B.*; 松元 達也*; 守田 幸路*; 福田 研二*; 鈴木 徹; 山野 秀将; 飛田 吉春

no journal, , 




角田 一樹; 竹田 幸治; 日下 翔太郎*; 小林 功佳*; 平原 徹*

no journal, , 


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