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論文

On the free surface boundary of moving particle semi-implicit method for thermocapillary flow

Wang, Z.; 杉山 智之

Engineering Analysis with Boundary Elements, 135, p.266 - 283, 2022/02

The moving particle semi-implicit (MPS) method has great potential in dealing with free surface flow due to its Lagrangian nature. In most cases, the free surface boundary is simply served as the pressure boundary condition. In this paper, an improved MPS method is presented for thermocapillary driven free surface flow. A series of surface nodes explicitly represent the free surface boundary. The normal stress on the free surface provides the Dirichlet pressure boundary condition, while the velocity boundary condition, i.e., Marangoni stress, is enforced through the Taylor series expansion and least squares method. Meanwhile, a quasi-Lagrangian formulation is introduced to avoid particle clustering and the corresponding numerical instability by slightly modifying the advection velocity. The upwind scheme is employed for the convection term to obtain accurate and stable results. A novel constraint scheme with the divergence of provisional velocity is developed for the pressure gradient to enhance stability further. The consistency of the derived generalized boundary condition is firstly verified with a simple convergence test. Then, several numerical tests, including square patch rotation, lid-driven and square droplet oscillation, are simulated to show the improvements. Finally, thermocapillary driven flows in an open cavity without and with buoyancy effect are studied. Good agreements are obtained by comparing with reference simulations taken from literature. Heat transfer characteristics are further investigated for different dimensionless numbers, including the Rayleigh number and Marangoni number.

論文

Temperature-dependent hardening contributions in CrFeCoNi high-entropy alloy

Naeem, M.*; He, H.*; Harjo, S.; 川崎 卓郎; Lin, W.*; Kai, J.-J.*; Wu, Z.*; Lan, S.*; Wang, X.-L.*

Acta Materialia, 221, p.117371_1 - 117371_18, 2021/12

We studied the deformation behavior of CrFeCoNi high-entropy alloy by in situ neutron diffraction at room temperature, intermediate low temperature of 140 K, low temperatures of 40 K (no serrated deformation) and 25 K (with massive serrations). The contributions from different deformation mechanisms to the yield strength and strain hardening have been estimated. The athermal contributions to the yield strength were $$sim$$183 MPa at all temperatures, while the Peierls stress increased significantly at low temperatures (from 148 MPa at room temperature to 493 MPa at 25 K). Dislocations contributed to $$sim$$94% strain hardening at room temperature. Although the dislocation strengthening remained the major hardening mechanism at very low temperatures, the planar faults contribution increased steadily from 6% at room temperature to 28% at 25 K.

論文

Evidence for strong correlations at finite temperatures in the dimerized magnet Na$$_{2}$$Cu$$_{2}$$TeO$$_{6}$$

Shangguan, Y.*; Bao, S.*; Dong, Z.-Y.*; Cai, Z.*; Wang, W.*; Huang, Z.*; Ma, Z.*; Liao, J.*; Zhao, X.*; 梶本 亮一; et al.

Physical Review B, 104(22), p.224430_1 - 224430_8, 2021/12

Dimerized magnets forming alternating Heisenberg chains exhibit quantum coherence and entanglement and thus can find potential applications in quantum information and computation. However, magnetic systems typically undergo thermal decoherence at finite temperatures. Here, we show inelastic neutron scattering results on an alternating antiferromagnetic-ferromagnetic chain compound Na$$_{2}$$Cu$$_{2}$$TeO$$_{6}$$ that the excited quasiparticles can counter thermal decoherence and maintain strong correlations at elevated temperatures. At low temperatures, we observe clear dispersive singlet-triplet excitations arising from the dimers formed along the crystalline $$b$$-axis. The excitation gap is of $$sim$$18 meV and the bandwidth is about half of the gap. The band top energy has a weak modulation along the [100] direction, indicative of a small interchain coupling. The gap increases while the bandwidth decreases with increasing temperature, leading to a strong reduction in the available phase space for the triplons. As a result, the Lorentzian-type energy broadening becomes highly asymmetric as the temperature is raised. These results are associated with a strongly correlated state resulting from hard-core constraint and quasiparticle interactions. We consider these results to be not only evidence for strong correlations at finite temperatures in Na$$_{2}$$Cu$$_{2}$$TeO$$_{6}$$, but also for the universality of the strongly correlated state in a broad range of quantum magnetic systems.

論文

The $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross section from the surrogate ratio method and its effect on the $$^{60}$$Fe nucleosynthesis

Yan, S. Q.*; Li, X. Y.*; 西尾 勝久; Lugaro, M.*; Li, Z. H.*; 牧井 宏之; Pignatari, M.*; Wang, Y. B.*; Orlandi, R.; 廣瀬 健太郎; et al.

Astrophysical Journal, 919(2), p.84_1 - 84_7, 2021/10

 被引用回数:0

The long-lived $$^{60}$$Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe on $$^{59}$$Fe (half-life=44.5 days) is the key reaction for the production of $$^{60}$$Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 $$gamma$$-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5$$pm$$3.5 mb at $$kT$$ = 30 keV and 13.4$$pm$$1.7 mb at $$kT$$ = 90 keV, roughly 10%-20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of $$^{60}$$Fe from the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe rate are at most 25$$%$$. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of $$^{60}$$Fe.

論文

Investigation of the ground-state spin inversion in the neutron-rich $$^{47,49}$$Cl isotopes

Linh, B. D.*; Corsi, A.*; Gillibert, A.*; Obertelli, A.*; Doornenbal, P.*; Barbieri, C.*; Chen, S.*; Chung, L. X.*; Duguet, T.*; G$'o$mez-Ramos, M.*; et al.

Physical Review C, 104(4), p.044331_1 - 044331_16, 2021/10

理化学研究所のRIビームファクトリーにて中性子過剰$$^{47,49}$$Clの励起状態を$$^{50}$$Arからのノックアウト反応によって生成し、脱励起ガンマ線からそのエネルギー準位を測定した。また、陽子ノックアウトの運動量分布から$$^{49}$$Clの基底状態が$$3/2^+$$であることがわかった。その結果を大規模殻模型計算およびいくつかの第一原理計算と比較した。$$^{47,49}$$Cl同位体の基底状態および第一励起状態は、計算で用いた相互作用に敏感であることがわかった。それは、陽子の一粒子エネルギーと四重極集団運動との複雑な結合によるためであると考えられる。

論文

Martensitic transformation in CrCoNi medium-entropy alloy at cryogenic temperature

Naeem, M.*; Zhou, H.*; He, H.*; Harjo, S.; 川崎 卓郎; Lan, S.*; Wu, Z.*; Zhu, Y.*; Wang, X.-L.*

Applied Physics Letters, 119(13), p.131901_1 - 131901_7, 2021/09

We investigated the in situ deformation behavior of the CrCoNi medium-entropy alloy at a cryogenic temperature of 140 K and compared it with deformation at room temperature. The sample exhibited higher strength and larger ductility at the cryogenic temperature. The CrCoNi alloy remained single-phase face-centered cubic at room temperature, while deformation at 140 K resulted in a martensitic transformation to the hexagonal close-packed structure. The phase transformation, an additional deformation mechanism to stacking faults, twinning, and dis- location slip, resulted in a higher work hardening at cryogenic temperature. The study addresses the structure metastability in the CrCoNi alloy, which led to the formation of epsilon-martensite from the intrinsic stacking faults.

論文

Pairing forces govern population of doubly magic $$^{54}$$Ca from direct reactions

Browne, F.*; Chen, S.*; Doornenbal, P.*; Obertelli, A.*; 緒方 一介*; 宇都野 穣; 吉田 数貴; Achouri, N. L.*; 馬場 秀忠*; Calvet, D.*; et al.

Physical Review Letters, 126(25), p.252501_1 - 252501_7, 2021/06

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

理化学研究所RIビームファクトリーにて、中性子過剰核$$^{55}$$Scからの1陽子ノックアウト反応によって$$^{54}$$Caを生成し、そのエネルギー準位と反応断面積をガンマ線分光および不変質量分光によって得た。その結果を歪曲波インパルス近似による核反応計算と大規模殻模型による核構造計算を組み合わせた理論値と比較した。実験の準位と断面積は理論計算によってよく再現された。$$^{54}$$Caの正パリティ状態については、基底状態の生成断面積が励起状態のものに比べて圧倒的に大きいという結果が得られた。これは、$$^{55}$$Scでは中性子魔法数34が消滅し$$^{54}$$Caではその魔法数が存在するというこれまでの知見と一見矛盾するが、対相関による分光学的因子のコヒーレンスから理解することができる。

論文

Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; 石川 喜久*; 鳥居 周輝*; 米村 雅雄*; 幸田 章宏*; 小松 一生*; 町田 真一*; 佐野 亜沙美; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

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

層状ペロブスカイトPrBaCo$$_{2}$$O$$_{5.5}$$は、熱膨張のない複合材料を作るために必要な負の熱膨張(NTE)を示す。NTEは、自発的な磁気秩序と密接に関連していることがわかっていた(磁気体積効果: MVE)。今回、われわれは、PrBaCo$$_{2}$$O$$_{5.5}$$の連続的な磁気体積効果が、本質的には不連続であり、大きな体積を持つ反強磁性絶縁体(AFILV)から、小さな体積をもつ強磁性卑絶縁体(FLISV)への磁気電気的相転移に起因することを明らかにした。また、磁気電気効果(ME)は、温度,キャリアドーピング,静水圧,磁場などの複数の外部刺激に対して高い感度を示した。これは、これまでよく知られている対称性の破れを伴う巨大磁気抵抗やマルチフェロイック効果などのMEとは対照的であり、輝コバルト鉱のMEは同一の結晶構造で起こる。われわれの発見は、MEとNTEを実現するための新しい方法を示しており、それは新しい技術に応用されるかもしれない。

論文

First spectroscopic study of $$^{51}$$Ar by the ($$p$$,2$$p$$) reaction

Juh$'a$sz, M. M.*; Elekes, Z.*; Sohler, D.*; 宇都野 穣; 吉田 数貴; 大塚 孝治*; 緒方 一介*; Doornenbal, P.*; Obertelli, A.*; 馬場 秀忠*; et al.

Physics Letters B, 814, p.136108_1 - 136108_8, 2021/03

 被引用回数:1 パーセンタイル:74.98(Astronomy & Astrophysics)

($$p$$,$$2p$$)反応と$$gamma$$線分光を用いて$$^{51}$$Arの束縛状態と非束縛状態の核構造研究を行った。実験結果と殻模型計算を比較することで、2つの束縛状態と6つの非束縛状態を決定した。$$^{51}$$Arの束縛状態を生成する反応断面積が小さいことから、これは中性子数32, 34の顕著なsub-shell closureが存在している確かな証拠と解釈できる。

論文

Stacking fault driven phase transformation in CrCoNi medium entropy alloy

He, H.*; Naeem, M.*; Zhang, F.*; Zhao, Y.*; Harjo, S.; 川崎 卓郎; Wang, B.*; Wu, X.*; Lan, S.*; Wu, Z.*; et al.

Nano Letters, 21(3), p.1419 - 1426, 2021/02

 被引用回数:3 パーセンタイル:0(Chemistry, Multidisciplinary)

In CrCoNi, a so-called medium-entropy alloy, an fcc-to-hcp phase transformation has long been anticipated. Here, we report an in situ loading study with neutron diffraction, which revealed a bulk fcc-to-hcp phase transformation in CrCoNi at 15 K under tensile loading. By correlating deformation characteristics of the fcc phase with the development of the hcp phase, it is shown that the nucleation of the hcp phase was triggered by intrinsic stacking faults. The confirmation of a bulk phase transformation adds to the myriads of deformation mechanisms available in CrCoNi, which together underpin the unusually large ductility at low temperatures.

論文

Chapter 18, Moving particle semi-implicit method

Wang, Z.; Duan, G.*; 越塚 誠一*; 山路 哲史*

Nuclear Power Plant Design and Analysis Codes, p.439 - 461, 2021/00

The Moving Particle Semi-implicit (MPS) method is one kind of particles methods which are based on Lagrangian approach. It has been developed to analyze complex thermal-hydraulic problems, including those in nuclear engineering. Since meshes are no longer used, large deformation of free surfaces or interfaces can be simulated without the problems of mesh distortion. This approach is effective in solving multiphase fluid dynamics which is subject to complex motion of free surfaces or interfaces. Since its development, MPS method has been extensively utilized for wide range of applications in nuclear engineering. In this chapter, the basic theory of the MPS method is firstly explained. Then, some examples of its application in nuclear engineering, including bubble dynamic, vapor explosion, jet breakup, multiphase flow instability, in-vessel phenomenon, molten spreading, molten core concrete interaction (MCCI) and flooding, are presented.

論文

General synthesis of single-atom catalysts for hydrogen evolution reactions and room-temperature Na-S batteries

Lai, W.-H.*; Wang, H.*; Zheng, L.*; Jiang, Q.*; Yan, Z.-C.*; Wang, L.*; 吉川 浩史*; 松村 大樹; Sun, Q.*; Wang, Y.-X.*; et al.

Angewandte Chemie; International Edition, 59(49), p.22171 - 22178, 2020/12

 被引用回数:16 パーセンタイル:89.25(Chemistry, Multidisciplinary)

Herein, we report a comprehensive strategy to synthesize a full range of single-atom metals on carbon matrix, including V, Mn, Fe, Co, Ni, Cu, Ge, Mo, Ru, Rh, Pd, Ag, In, Sn, W, Ir, Pt, Pb, and Bi. The extensive applications of various single-atom catalysts (SACs) are manifested via their ability to electro-catalyze typical hydrogen evolution reactions (HER) and conversion reactions in novel room-temperature sodium sulfur batteries (RT-Na-S). The enhanced performances for these electrochemical reactions arisen from the ability of different single active atoms on local structures to tune their electronic configuration. Significantly, the electrocatalytic behaviors of diverse SACs, assisted by density functional theory calculations, are systematically revealed by in situ synchrotron X-ray diffraction and in situ transmission electronic microscopy, providing a strategic library for the general synthesis and extensive applications of SACs in energy conversion and storage.

論文

$$N$$ = 32 shell closure below calcium; Low-lying structure of $$^{50}$$Ar

Cort$'e$s, M. L.*; Rodriguez, W.*; Doornenbal, P.*; Obertelli, A.*; Holt, J. D.*; Men$'e$ndez, J.*; 緒方 一介*; Schwenk, A.*; 清水 則孝*; Simonis, J.*; et al.

Physical Review C, 102(6), p.064320_1 - 064320_9, 2020/12

 被引用回数:1 パーセンタイル:35.83(Physics, Nuclear)

理化学研究所RIBFにおいて、$$N$$=32同位体である$$^{50}$$Arの低励起構造を陽子・中性子ノックアウト反応,多核子剥離反応,陽子非弾性散乱と$$gamma$$線分光によって調査した。すでに知られていた2つに加えて、3$$^{-}$$状態の候補を含む5つの状態を新たに確認した。$$gamma$$ $$gamma$$ coincidenceによって得られた準位図は$$sd-pf$$模型空間での殻模型計算やカイラル2体・3体力による第一原理計算と比較した。陽子・中性子ノックアウト反応断面積の理論との比較により、新たに発見された2つの状態は2$$^{+}$$状態であり、また以前に4$$^{+}_{1}$$とされていた状態も2$$^{+}$$であることが示唆された。

論文

Consistent robin boundary enforcement of particle method for heat transfer problem with arbitrary geometry

Wang, Z.; Duan, G.*; 松永 拓也*; 杉山 智之

International Journal of Heat and Mass Transfer, 157, p.119919_1 - 119919_20, 2020/08

 被引用回数:3 パーセンタイル:65.8(Thermodynamics)

Enforcing accurate and consistent boundary conditions is a difficult issue for particle methods, due to the lack of information outside boundaries. Recently, consistent Neumann boundary condition enforcement is developed for the least squares moving particle semi-implicit method (LSMPS). However, the Robin boundary cannot be straightforwardly considered by that method because no computational variables are defined on the wall boundary. In this paper, a consistent Robin boundary enforcement for heat transfer problem is proposed. Based on the Taylor series expansion, the Robin boundary condition for temperature is converted to the fitting function of internal rather than boundary particles and incorporated into least squares approach for discretization schemes. Arbitrary geometries can be easily treated due to the use of polygons for wall boundary. A convergence study was firstly carried out to verify the consistency. Then, numerical tests of 1-D and 2-D heat conduction problems subjected to mixed boundary conditions were performed for verification, and good agreements with theoretical solutions were observed. Natural convection problems with different boundary conditions in an annulus were carried out for further validations of heat-fluid coupling. Excellent agreements between the present and literature results were demonstrated.

論文

Strong lattice anharmonicity exhibited by the high-energy optical phonons in thermoelectric material

Wu, P.*; Fan, F.-R.*; 萩原 雅人*; 古府 麻衣子; Peng, K.*; 石川 喜久*; Lee, S.*; 本田 孝志*; 米村 雅雄*; 池田 一貴*; et al.

New Journal of Physics (Internet), 22(8), p.083083_1 - 083083_9, 2020/08

 被引用回数:2 パーセンタイル:51.78(Physics, Multidisciplinary)

熱電材料SnSeは、過去数年間で世界的な関心を呼び、その固有の強い格子非調和性は、その優れた熱電性能の重要な要素と見なされている。一方、SnSeにおける格子非調和性の理解は、特にフォノンダイナミクスがこの動作によってどのように影響を受けるかに関して、依然として不十分である。そのため、中性子全散乱,非弾性中性子散乱,ラマン分光法、および凍結フォノン計算により、Na$$_{0.003}$$Sn$$_{0.997}$$Se$$_{0.9}$$S$$_{0.1}$$の格子力学の包括的な研究を行った。格子非調和性は、対分布関数,非弾性中性子散乱、およびラマン測定によって確かめられた。熱膨張と多重フォノン散乱の影響を分離することにより、後者は高エネルギー光学フォノンモードで非常に重要であることがわかった。フォノンモードの強い温度依存性は、この系の非調和性を示している。さらに、我々のデータは、Sドーピングにより、高エネルギー光学フォノンの線幅が広がることを明らかにした。私たちの研究は、SnSeの熱電性能は、フォノンエンジニアリングを介して格子熱伝導率への高エネルギー光学フォノンモードの寄与を減らすことによってさらに強化できることを示唆する。

論文

Production of $$^{266}$$Bh in the $$^{248}$$Cm($$^{23}$$Na,5$$n$$)$$^{266}$$Bh reaction and its decay properties

羽場 宏光*; Fan, F.*; 加治 大哉*; 笠松 良崇*; 菊永 英寿*; 小森 有希子*; 近藤 成美*; 工藤 久昭*; 森本 幸司*; 森田 浩介*; et al.

Physical Review C, 102(2), p.024625_1 - 024625_12, 2020/08

 被引用回数:2 パーセンタイル:57.67(Physics, Nuclear)

The nuclide $$^{266}$$Bh was produced in the $$^{248}$$Cm($$^{23}$$Na,5n)$$^{266}$$Bh reaction at beam energies of 125.9, 130.6, and 135.3 MeV. Decay properties of $$^{266}$$Bh were investigated with a rotating wheel apparatus for $$alpha$$ and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. The half-life of $$^{266}$$Bh was measured to be $$T_{rm 1/2}$$ = 10.0$$^{+2.6}_{-1.7}$$ s. The $$alpha$$-particle energies of $$^{266}$$Bh disperse widely in the range of 8.62 - 9.40 MeV. The maximum production cross section for the $$^{248}$$Cm($$^{23}$$Na,5n)$$^{266}$$Bh reaction was determined to be $$sigma$$ = 57 $$pm$$ 14 pb at 130.6 MeV.

論文

Development of a multiphase particle method for melt-jet breakup behavior of molten core in severe accident

Wang, Z.; 岩澤 譲; 杉山 智之

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 12 Pages, 2020/08

In a hypothetical severe accident in a light water reactor (LWR) nuclear power plant, there is a possibility that molten core released from the reactor vessel gets in contact with water in the containment vessel. In this so-called fuel-coolant interactions (FCIs) process, the melt jet will breakup into fragments, which is one of the important factors for a steam explosion, as a potential threat to the integrity of the containment vessel. In order to investigate the melt-jet breakup with solidification processes, a multiphase particle method is developed in this study. Benefiting from its Lagrangian description and meshless framework, the large deformed interfaces could be directly and easily captured by the particle motions. A simple transient heat conduction test is firstly carried out. Two important multiphase instabilities, namely the Rayleigh-Taylor instability and the Kelvin-Helmholtz instability, are studied since they play important roles during the melt-jet breakup. After that, a bubble rising benchmark is performed to show the feasibility of modelling for deformation and collapse. The results achieved so far indicates that the developed particle method is capable to analyze the melt-jet breakup with solidification processes.

論文

Evidence for magnon-phonon coupling in the topological magnet Cu$$_{3}$$TeO$$_{6}$$

Bao, S.*; Cai, Z.*; Si, W.*; Wang, W.*; Wang, X.*; Shangguan, Y.*; Ma, Z.*; Dong, Z.-Y.*; 梶本 亮一; 池内 和彦*; et al.

Physical Review B, 101(21), p.214419_1 - 214419_8, 2020/06

 被引用回数:4 パーセンタイル:68.88(Materials Science, Multidisciplinary)

We perform thermodynamic and inelastic neutron scattering (INS) measurements to study the lattice dynamics (phonons) of a cubic collinear antiferromagnet Cu$$_{3}$$TeO$$_{6}$$ which hosts topological spin excitations (magnons). While the specific heat and thermal conductivity results show that the thermal transport is dominated by phonons, the deviation of the thermal conductivity from a pure phononic model indicates that there is a strong coupling between magnons and phonons. In the INS measurements, we find a mode in the excitation spectra at 4.5 K, which exhibits a slight downward dispersion around the Brillouin zone center. This mode disappears above the N$'{e}$el temperature and thus cannot be a phonon. Furthermore, the dispersion is distinct from that of a magnon. Instead, it can be explained by the magnon-polaron mode, collective excitations resulting from the hybridization between magnons and phonons. We consider the suppression of the thermal conductivity and emergence of the magnon-polaron mode to be evidence for magnon-phonon coupling in Cu$$_{3}$$TeO$$_{6}$$.

論文

Magnetic-field and composition tuned antiferromagnetic instability in the quantum spin-liquid candidate NaYbO$$_2$$

Guo, J.*; Zhao, X.*; 河村 聖子; Ling, L.*; Wang, J.*; He, L.*; 中島 健次; Li, B.*; Zhang, Z.*

Physical Review Materials (Internet), 4(6), p.064410_1 - 064410_7, 2020/06

 被引用回数:4 パーセンタイル:51.8(Materials Science, Multidisciplinary)

NaYbO$$_2$$ has been reported as a possible host for the quantum spin-liquid state. Here, the composition-dependent polycrystalline Na$$_{1-x}$$YbO$$_2$$ ($$x = 0$$, 0.03, and 0.07) has been investigated by combining high-field magnetizations and inelastic neutron scattering techniques. For the $$x = 0$$ sample, no signature of a magnetic order is observed down to 0.3 K. Inelastic neutron scattering measurement suggests a continuous low-energy excitation spectrum centered at momentum transfer $$(Q) sim 1.25$$~$AA$^{-1}$$ and extending up to energy transfer $$(E) sim 2.0$$~meV. In contrast, $$x = 0.03$$ and 0.07 samples exhibit magnetic transitions at 1.1 and 2.3 K, respectively. High-field magnetization measurements indicate similar behaviors for $$x = 0$$ and 0.03 samples including plateau-like features at the 1/3 saturated magnetization, which implies that the spin disorder in the $$x = 0$$ sample might be suppressed preceding the emergence of the up-up-down phase. This composition- and field-dependent study allows us to construct complete phase diagrams indicating that NaYbO$$_2$$ is a promising candidate for the quantum spin-liquid state in close proximity to the antiferromagnetic instability tuned by the application of magnetic fields as well as controlling the concentration of Na$$^+$$ ion vacancies.

論文

Spin dynamics of a magnetic Weyl semimetal Sr$$_{1-x}$$Mn$$_{1-y}$$Sb$$_{2}$$

Cai, Z.*; Bao, S.*; Wang, W.*; Ma, Z.*; Dong, Z.-Y.*; Shangguan, Y.*; Wang, J.*; Ran, K.*; Li, S.*; 蒲沢 和也*; et al.

Physical Review B, 101(13), p.134408_1 - 134408_10, 2020/04

 被引用回数:2 パーセンタイル:24.67(Materials Science, Multidisciplinary)

ディラック物質は量子現象と共にキャリアの役割を探索するのに良い系で、磁気ワイル半金属のSr$$_{1-x}$$Mn$$_{1-y}$$Sb$$_{2}$$はワイルフェルミオンとマグノンの関係を研究する良い舞台である。本研究では、Sr$$_{1-x}$$Mn$$_{1-y}$$Sb$$_{2}$$の単結晶の中性子非弾性散乱実験を行い、磁性Mn層の分散は約76meVまで広がり、層間の分散は6meVの狭いバンド幅を持つことを見出した。また、これらの実験結果はハイゼンベルグ・スピンハミルトニアンを用いた線形スピン波理論によって再現可能である。本研究では、ワイルフェルミオンとマグノンが共存しているにもかかわらず、Sr$$_{1-x}$$Mn$$_{1-y}$$Sb$$_{2}$$中のワイルフェルミオンが磁気ダイナミクスに影響を与えているという明確な証拠は得られなかった。これは、ワイルフェルミオンとマグノンがSb層とMn層に別々に存在し、この擬二次元性による層間結合の弱さに起因するもの考えられる。

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