The Role of silicon on solute clustering and embrittlement in highly neutron-irradiated pressurized water reactor surveillance test specimens

高見澤 悠; 端 邦樹; 西山 裕孝; 外山 健*; 永井 康介*

Journal of Nuclear Materials, 556, p.153203_1 - 153203_10, 2021/12

https://doi.org/10.1016/j.jnucmat.2021.153203

原子炉圧力容器鋼における中性子照射脆化に及ぼすシリコンの影響を明らかにするため、三次元アトムプローブにより、高照射量領域まで中性子照射された監視試験片中の溶質原子クラスタを分析した。高Cu含有材では、Ni, Mn, Siがクラスタ中心のCu原子を囲むように凝集し、コアシェル構造を形成するのに対して、低Cu含有材ではNi, Mn, Siがクラスタ中を均一に分布していた。クラスタ内のCu原子の数はCu含有量の減少と共に減少したが、それを補うようにSi原子数が増加した。材料中の公称のSi含有量の増加とともに、クラスタのギニエ半径は減少し、数密度が増加した。結果として、クラスタの体積率は一定であった。延性脆性遷移温度移行量とクラスタの体積率とギニエ半径の積の平方根が良い相関関係を示すことから、脆化の主要因は、溶質原子クラスタを転位が切断するメカニズムによる硬化であることが示された。また、Si含有量の増加により、クラスタの体積率は一定のままギニエ半径が減少することで脆化の程度を減少させることが示された。

Gapless spin liquid in a square-kagome lattice antiferromagnet

藤原 理賀*; 森田 克洋*; Mole, R.*; 満田 節生*; 遠山 貴巳*; 矢野 真一郎*; Yu, D.*; 曽田 繁利*; 桑井 智彦*; 幸田 章宏*; et al.

Nature Communications (Internet), 11(1), p.3429_1 - 3429_7, 2020/07

https://doi.org/10.1038/s41467-020-17235-z

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two-dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCuAlBiO(SO)Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation, and inelastic neutron scattering measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state.

Magnetic phase diagram of a frustrated spin ladder

杉本 貴則*; 森 道康; 遠山 貴己; 前川 禎通

Physical Review B, 97(14), p.144424_1 - 144424_10, 2018/04

AA2018-0074.pdf:1.54MB

https://doi.org/10.1103/PhysRevB.97.144424

Frustrated spin ladders show magnetization plateaux depending on the rung-exchange interaction and frustration defined by the ratio of first and second neighbor exchange interactions in each chain. This paper reports on its magnetic phase diagram. Using the variational matrix-product state method, we accurately determine phase boundaries. Several kinds of magnetization plateaux are induced by the frustration and the strong correlation among quasiparticles on a lattice. The appropriate description of quasiparticles and their relevant interactions are changed by a magnetic field. We find that the frustration differentiates the triplet quasiparticle from the single tone in kinetic energy.

Predoping effects of boron and phosphorous on arsenic diffusion along grain boundaries in polycrystalline silicon investigated by atom probe tomography

高見澤 悠; 清水 康雄*; 井上 耕治*; 野沢 康子*; 外山 健*; 矢野 史子*; 井上 真雄*; 西田 彰男*; 永井 康介*

Applied Physics Express, 9(10), p.106601_1 - 106601_4, 2016/10

https://doi.org/10.7567/APEX.9.106601

The effect of phosphorus (P) and boron (B) doping on arsenic (As) diffusion in polycrystalline silicon (poly-Si) was investigated using laser-assisted atom probe tomography. In all samples, a high concentration of As was found at the grain boundaries, indicating that such boundaries represent the main diffusion path. However, As grain-boundary diffusion was suppressed in the B-doped sample, and enhanced in the P-doped sample. In a sample co-doped with both P and B, As diffusion was somewhat enhanced, indicating competition between the effects of the two dopants. This can be explained by the pairing of P and B atoms. The results suggest that grain-boundary diffusion of As can be controlled by varying the local concentration of P and B dopants.

Orbital-selective electronic excitations in iron arsenides revealed by simulated nonresonant inelastic X-ray scattering

筒井 健二; 兼下 英司*; 遠山 貴巳*

Physical Review B, 92(19), p.195103_1 - 195103_5, 2015/11

https://doi.org/10.1103/PhysRevB.92.195103

非共鳴非弾性X線散乱(NIXS)は電子系の電荷励起を検知する手段としての可能性をもっている。さらに、X線の大きな運動量変化領域における多極子遷移によって、多軌道系遍歴3d電子系の軌道選択された電子励起を決められる可能性が生まれた。その例として鉄砒素系化合物の反強磁性状態を挙げ、NIXSの適切な運動量変化を選ぶことにより、軌道が選択された励起を検知できることを理論的に明らかにする。多軌道系遍歴電子系における軌道励起の本質を理解する上で、NIXSと共鳴非弾性X線散乱がいかにお互いに補い合うかを示す。

Magnetization plateaus by reconstructed quasispinons in a frustrated two-leg spin ladder under a magnetic field

杉本 貴則*; 森 道康; 遠山 貴巳*; 前川 禎通

Physical Review B, 92(12), p.125114_1 - 125114_6, 2015/09

AA2015-0451.pdf:0.43MB

https://doi.org/10.1103/PhysRevB.92.125114

The quantum phase transitions induced by a magnetic field are theoretically studied in a frustrated two-leg spin ladder. Using the density-matrix renormalization-group method, we find some magnetic phase transitions and plateaux in two different cases of strong and weak rung couplings. With the strong rung coupling, the three magnetization plateaux are found at 1/3, 1/2, and 2/3 due to the frustration. Those can be understood in terms of a quasi-spinon reconstructed from the singlet and the triplets of spins on a rung. The plateau at 1/2 corresponds to the valence bond solid of the quasispinons, while the plateaux at 1/3 and 2/3 can be associated with the array of quasi-spinons such as soliton lattice. This is different from the usual Bose-Einstein-condensation picture of triplons. Our results will be useful to understand magnetization curves in BiCuPO.

Theoretical study of electronic states and excitation spectra in Ni-substituted cuprates

筒井 健二; 遠山 貴己*; 前川 禎通

JPS Conference Proceedings (Internet), 3, p.017008_1 - 017008_6, 2014/06

https://doi.org/10.7566/JPSCP.3.017008

銅酸化物高温超伝導物質における不純物置換効果の研究がこれまで世界中で数多く研究されている。Ni不純物置換に対してキャリアがNi不純物近傍へ局在化するといった興味深い現象が実験及び理論的研究により明らかになってきている。本研究ではクラスター計算によって、不純物濃度に比べてホール濃度が高い場合の電子状態を議論し、共鳴非弾性X線散乱スペクトルの予見を行った。

High-energy spin and charge excitations in electron-doped copper oxide superconductors

石井 賢司; 藤田 全基*; 佐々木 隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山 貴己*; et al.

Nature Communications (Internet), 5, p.3714_1 - 3714_8, 2014/04

https://doi.org/10.1038/ncomms4714

We combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone center and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the -point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin-excitations (paramagnons) recently observed in hole-doped compounds even at high doping-levels.

Spin dynamics and resonant inelastic X-ray scattering in chromium with commensurate spin-density wave order

杉本 高大*; Li, Z.*; 兼下 英司*; 筒井 健二; 遠山 貴己*

Physical Review B, 87(13), p.134418_1 - 134418_8, 2013/04

https://doi.org/10.1103/PhysRevB.87.134418

多軌道系反強磁性金属であるクロム金属のスピン励起スペクトルと共鳴非弾性X線散乱スペクトルを理論的に予見した。スペクトルの計算に際し、多軌道ハバード模型に対する平均場近似及び乱雑位相近似を行い、またX線散乱プロセスに対して高速衝突近似を行った。その結果、スピン励起に関しては、0.6eV以上で集団励起であるマグノン励起がほとんど強度を持たず、代わりに個別励起のエネルギー的に広がったスペクトルが支配的になることがわかった。

Inelastic X-ray scattering studies of electronic excitations

石井 賢司; 遠山 貴己*; 水木 純一郎

Journal of the Physical Society of Japan, 82(2), p.021015_1 - 021015_24, 2013/02

https://doi.org/10.7566/JPSJ.82.021015

Inelastic X-ray Scattering (IXS) has developed as one of the most powerful momentum-resolved spectroscopies. Especially in the last decade, it achieved significant progress by utilizing brilliant X-rays from third generation synchrotron radiation facilities. Simultaneously, theoretical efforts have been made to predict or interpret the experimental spectra. One of the scientific fields studied intensively by means of IXS is strongly correlated electron systems, where the interplay of charge, spin, and orbital degrees of freedom determines their physical properties. IXS can provide a new insight into electron dynamics of the systems through the observation of charge, spin, and orbital excitations. Focusing on the momentum-resolved electronic excitations in strongly correlated electron systems, we review IXS studies and present capabilities of IXS for the study of dynamics of materials.