JOPSS:検索結果一覧

検索結果：　143 件中 1件目～20件目を表示

1
2
3
4
5
・・・
8
>

発表形式

Initialising ...

選択項目を絞り込む

掲載資料名

Initialising ...

発表会議名

Initialising ...

筆頭著者名

Initialising ...

キーワード

Initialising ...

使用言語

Initialising ...

発行年

Initialising ...

開催年

Initialising ...

論文

Magnetic excitation in the =1/2 Ising-like antiferromagnetic chain CsCoCl $_{3}$ in longitudinal magnetic fields studied by high-field ESR measurements

木村尚次郎*; 大西弘明; 奥西巧一*; 赤木暢*; 鳴海康雄*; 萩原政幸*; 金道浩一*; 菊池彦光*

Journal of the Physical Society of Japan, 92(9), p.094701_1 - 094701_9, 2023/09

https://doi.org/10.7566/JPSJ.92.094701

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

High-field electron spin resonance (ESR) measurements were performed on the =1/2 Ising-like antiferromagnetic chain CsCoCl $_{3}$ in the frequency range up to 4.4THz and magnetic fields for up to 53T. We observed softening of the spinon excitation, which drives the spin chain into the quantum critical state at the critical field $H_{c}$ =33.0T. Above $H_{c}$ , we observed the string excitation at the wave number =, which is characteristic of the =1/2 spin chain in the quantum critical state in the magnetic fields. We also observed a crossover of the string excitation to the magnon bound state above the saturation fields $H_{s}$ =43.9T upon increasing the magnetic fields. Finally, we discuss how the string excitation and magnon bound state can be excited by the electric dipole transition due to spin quadrupolar resonance.

論文

Low temperature behavior of itinerant ferromagnet realized in extended Nagaoka mechanism

大西弘明; 宮下精二*

JPS Conference Proceedings (Internet), 38, p.011157_1 - 011157_6, 2023/05

https://doi.org/10.7566/JPSCP.38.011157

We have proposed a Hubbard model which exhibits itinerant ferromagnetism by extending the model of Nagaoka ferromagnetism. In the present work, we confirm that the idea of the realization of itinerant ferromagnetism works in two- and three-dimensional lattices as well as a one-dimensional lattice which we studied previously. We also investigate the temperature dependence of the magnetic ordering and present a magnetic phase diagram in the space of the temperature and the chemical potential. In the obtained phase diagram, we find a V-shape structure for the magnetic ordering near a quantum phase transition. Besides, we find an additional peak exhibiting a dome structure. Temperature dependences of related spin correlation functions are studied in detail.

論文

Finite-temperature properties of extended Nagaoka ferromagnetism; Ordering processes and precursor of a quantum phase transition between itinerant ferromagnetic and Mott antiferromagnetic states

大西弘明; 宮下精二*

Physical Review B, 106(13), p.134436_1 - 134436_13, 2022/10

https://doi.org/10.1103/PhysRevB.106.134436

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

We study finite-temperature properties of a Hubbard model including sites of a particle bath which was proposed as a microscopic model to show itinerant ferromagnetism at finite electron density. We use direct numerical methods, such as exact diagonalization and random vector methods. The temperature dependence of quantities is surveyed in the full range of the temperature. We find that the specific heat has several peaks, which correspond to ordering processes in different energy scales. In particular, magnetic correlations develop at very low temperature. The system exhibits an itinerant ferromagnetic state or an antiferromagnetic state of the Mott insulator depending on the chemical potential of the particle bath and the Coulomb interaction. From a microscopic viewpoint, the competition between these two types of magnetic states causes a peculiar ordering process of local spin correlations. Some local ferromagnetic correlations are found to be robust, which indicates that the ferromagnetic correlation originates from the motion of itinerant electrons in a short-range cluster.

論文

Sodium-cooled Fast Reactors

大島宏之; 森下正樹*; 相澤康介; 安藤勝訓; 芦田貴志; 近澤佳隆; 堂田哲広; 江沼康弘; 江連俊樹; 深野義隆; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

https://shop.elsevier.com/books/sodium-cooled-fast-reactors/morishita/978-0-12-824076-2

ナトリウム冷却高速炉(SFR: Sodium-cooled Fast Reactor)の歴史や、利点、課題を踏まえた安全性、設計、運用、メンテナンスなどについて解説する。AIを利用した設計手法など、SFRの実用化に向けた設計や研究開発についても述べる。

論文

Excitation and transport of bound magnon clusters in frustrated ferromagnetic chain

大西弘明

Journal of Physics; Conference Series, 2207, p.012045_1 - 012045_6, 2022/03

https://doi.org/10.1088/1742-6596/2207/1/012045

By exploiting density-matrix renormalization group methods, we study magnetic and transport properties of a frustrated quantum spin chain with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions in an applied magnetic field. In high magnetic fields, there appear a series of spin multipole liquid ground states such as quadrupole, octupole, and hexadecapole, which are two-, three-, and four-magnon bound states, respectively. Since the low-energy excitation is governed by multi-magnon bound states, we envisage that bound magnon clusters would carry spin current. We will report detailed analyses of multipole excitation spectra and current correlation functions, and discuss how the magnon clusters contribute to the transport.

論文

Optical selection rules of the magnetic excitation in the = $frac{1}{2}$ one-dimensional Ising-like antiferromagnet BaCo $_{2}$ V $_{2}$ O $_{8}$

木村尚次郎*; 大西弘明; 奥谷顕*; 赤木暢*; 鳴海康雄*; 萩原政幸*; 奥西巧一*; 金道浩一*; He, Z.*; 谷山智康*; et al.

Physical Review B, 105(1), p.014417_1 - 014417_9, 2022/01

https://doi.org/10.1103/PhysRevB.105.014417

被引用回数：3 パーセンタイル：34.67(Materials Science, Multidisciplinary)

In this study, we clarify the selection rules of optical transitions from the ground state to the magnetic excited states in the quasi-one-dimensional quantum Ising-like antiferromagnet BaCo $_{2}$ V $_{2}$ O $_{8}$ with spin = $frac{1}{2}$ using the high-field electron spin resonance measurement with illuminating polarized electromagnetic waves. We demonstrate that the unconventional magnetic excitation via the pair creation of quasipaticles at wave numbers $q_{z}=pi/2$ and in the field-induced quantum critical state can couple with both oscillating magnetic and electric fields. Our density matrix renormalization group calculations indicate that the observed selection rules can be explained by two- and four-fold periodical spin interactions, originating from the screw chain structure in BaCo $_{2}$ V $_{2}$ O $_{8}$ , in addition to the magnetoelectric coupling between spins and electric dipoles.

論文

Spin excitations of the =1/2 one-dimensional Ising-like antiferromagnet BaCo $_{2}$ V $_{2}$ O $_{8}$ in transverse magnetic fields

奥谷顕*; 大西弘明; 木村尚次郎*; 竹内徹也*; 木田孝則*; 森道康; 三宅厚志*; 徳永将史*; 金道浩一*; 萩原政幸*

Journal of the Physical Society of Japan, 90(4), p.044704_1 - 044704_9, 2021/04

https://doi.org/10.7566/JPSJ.90.044704

被引用回数：3 パーセンタイル：30.35(Physics, Multidisciplinary)

The high-field multifrequency electron spin resonance (ESR), the magnetization, and the specific heat of single crystals of BaCo $_{2}$ V $_{2}$ O $_{8}$ (a quasi-one-dimensional Ising-like antiferromagnet with ) were measured in two different transverse magnetic fields: and . A softening of the lowest ESR mode was observed near the saturation field of the magnetization around 40 T in , whereas it occurs around 10 T in , far below the saturation field. These observations were reproduced by numerical calculations using the density-matrix renormalization group methods, including the staggered magnetic fields induced by a uniform external magnetic field and the interchain magnetic exchange interaction. We found that the directional dependence of the lowest mode originates mainly from the remarkable angular dependence of the induced magnetic field. The interchain interaction is also quantitatively important for reproducing the experimental results. The directional dependence of the lowest mode is demonstrated by the particle-hole excitation of spinons using the Jordan-Wigner transformation.

論文

Magnetic excitations and transport properties in frustrated ferromagnetic chain

大西弘明

Journal of Magnetism and Magnetic Materials, 479, p.88 - 90, 2019/06

https://doi.org/10.1016/j.jmmm.2019.02.006

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

In a spin nematic state of a spin-1/2 frustrated ferromagnetic chain, low-energy excitations are governed by bound magnons, so that bound magnons carry spin current and thermal current. Regarding magnetic excitations, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-range longitudinal and short-range transverse spin correlations, respectively, while we observe gapless quadrupole excitations, signaling quasi-long-range quadrupole correlations. In the present work, we investigate spin and thermal transport properties by exploiting numerical methods, such as exact diagonalization and density-matrix renormalization group. We will discuss the effects of bound magnon propagation in spin and thermal transport, based on detailed analyses of current-current correlation functions in the spin nematic ground state, and temperature and field dependencies of the spin Drude weight and the thermal Drude weight.

論文

Electrochemical reaction mechanisms under various charge-discharge operating conditions for Li $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ in a lithium-ion battery

小西宏明*; 平野辰巳*; 高松大郊*; 軍司章*; Feng, X.*; 古月翔*; 奥村壮文*; 寺田尚平*; 田村和久

Journal of Solid State Chemistry, 262, p.294 - 300, 2018/06

https://doi.org/10.1016/j.jssc.2018.03.028

被引用回数：9 パーセンタイル：49.17(Chemistry, Inorganic & Nuclear)

Li $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ 正極の充電過程において、各SOCでの電極電位は、放電過程より高い。この機構を明らかにするために、様々なSOCにおいて電気化学測定、XRD, XAFS測定を行った。その結果、Li $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ の格子状数や遷移金属の酸化状態が異なっていることが分かった。また、Li $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ 中に、LiNi $_{0.33}$ Mn $_{0.33}$ Co $_{0.33}$ O $_{2}$ やLi $_{2}$ MnO $_{3}$ に類似した構造が存在することも明らかになった。

論文

Dynamical quadrupole structure factor of frustrated ferromagnetic chain

大西弘明

Physica B; Condensed Matter, 536, p.346 - 349, 2018/05

https://doi.org/10.1016/j.physb.2017.10.056

被引用回数：2 パーセンタイル：10.36(Physics, Condensed Matter)

In a spin-1/2 $J_{1}$ - $J_{2}$ Heisenberg chain with ferromagnetic $J_{1}$ and antiferromagnetic $J_{2}$ , the ground state in high magnetic fields is a quadrupole state, the so-called spin nematic state. To understand the properties of the spin nematic state from the viewpoint of excitation dynamics, we have studied dynamical spin structure factors by density-matrix renormalization group methods. In the spin nematic regime, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-ranged longitudinal and short-ranged transverse spin correlations, respectively. These features can be examined by inelastic neutron scattering experiments. However, they are indirect evidence for the spin nematic state. Here, we proceed to analyze dynamical quadrupole structure factors to clarify excitation dynamics in the quadrupole channel. We observe gapless excitations at =, signaling quasi-long-ranged antiferro-quadrupole correlations. Information of spectral intensity distribution would be useful to discuss how we can detect the spin nematic state directly by experiments.

論文

Mechanisms responsible for two possible electrochemical reactions in Li $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ used for lithium ion batteries

小西宏明*; 平野辰巳*; 高松大郊*; 軍司章*; Feng, X.*; 古月翔*; 奥村壮文*; 寺田尚平*; 田村和久

Journal of Solid State Chemistry, 258, p.225 - 231, 2018/02

https://doi.org/10.1016/j.jssc.2017.10.024

被引用回数：8 パーセンタイル：44.83(Chemistry, Inorganic & Nuclear)

リチウムイオン電池の正極材料であるLi $_{1.2}$ Ni $_{0.13}$ Mn $_{0.54}$ Co $_{0.13}$ O $_{2}$ について、充放電過程における構造変化について調べた。実験結果から、充電過程ではSOCが大きくなるとともに、Li $_{2}$ MnO $_{3}$ ,LiNi $_{0.33}$ Mn $_{0.33}$ Co $_{0.33}$ O $_{2}$ ,Li $_{2}$ MnO $_{3}$ の順に結構構造が変化するのに対して、放電過程では、Li $_{2}$ MnO $_{3}$ ,LiNi $_{0.33}$ Mn $_{0.33}$ Co $_{0.33}$ O $_{2}$ の順に結晶構造が変化することが分かった。

論文

Neutron scattering study of yttrium iron garnet

社本真一; 伊藤孝; 大西弘明; 山内宏樹; 稲村泰弘; 松浦直人*; 赤津光洋*; 樹神克明; 中尾朗子*; 茂吉武人*; et al.

Physical Review B, 97(5), p.054429_1 - 054429_9, 2018/02

https://doi.org/10.1103/PhysRevB.97.054429

被引用回数：18 パーセンタイル：65.6(Materials Science, Multidisciplinary)

イットリウム鉄ガーネットの核および磁気構造と全マグノン分散を中性子散乱により調べた。低エネルギーの分散は強磁性マグノンで期待されるように14meVまで2次関数の分散を示した。積分した動的磁化率"()の虚部は低エネルギーで平方根のエネルギー依存性を示した。"()から絶対値でマグノン状態密度を求めた。その値は理論的に予想されるマグノン分散でひとつのカラリティーモードに対応する。

論文

Quantum phase transitions driven by rhombic-type single-ion anisotropy in the =1 Haldane chain

Tzeng, Y.-C.*; 大西弘明; 大久保毅*; Kao, Y.-J.*

Physical Review B, 96(6), p.060404_1 - 060404_7, 2017/08

https://doi.org/10.1103/PhysRevB.96.060404

被引用回数：24 パーセンタイル：72.72(Materials Science, Multidisciplinary)

The spin-1 Haldane chain is an example of the symmetry-protected-topological (SPT) phase in one dimension. Experimental realization of the spin chain materials usually involves both the uniaxial-type, , and the rhombic-type, , single-ion anisotropies. Here, we provide a precise ground-state phase diagram for a spin-1 Haldane chain with these single-ion anisotropies. Using quantum numbers, we find that the symmetry breaking phase can be characterized by double degeneracy in the entanglement spectrum. Topological quantum phase transitions take place on particular paths in the phase diagram, from the Haldane phase to the large-, large-, or large- phases. The topological critical points are determined by the level spectroscopy method with a newly developed parity technique in the density matrix renormalization group, and the Haldane-large- critical point is obtained with an unprecedented precision, =0.9684713(1). Close to this critical point, a small rhombic single-ion anisotropy can destroy the Haldane phase and bring the system into a -Nel phase. We propose that the compound [Ni(HF)(3-Clpy)]BF is a candidate system to search for the -Nel phase.

論文

Magnetic structure and dispersion relation of the =1/2 quasi-one-dimensional Ising-like antiferromagnet BaCo $_{2}$ V $_{2}$ O $_{8}$ in a transverse magnetic field

松田雅昌*; 大西弘明; 奥谷顕*; Ma, J.*; Agrawal, H.*; Hong, T.*; Pajerowski, D. M.*; Copley, J. R. D.*; 奥西巧一*; 森道康; et al.

Physical Review B, 96(2), p.024439_1 - 024439_8, 2017/07

https://doi.org/10.1103/PhysRevB.96.024439

被引用回数：12 パーセンタイル：51.46(Materials Science, Multidisciplinary)

BaCo $_{2}$ V $_{2}$ O $_{8}$ consists of Co chains, in which Co $^{2+}$ ion carries a fictitious spin $frac{1}{2}$ with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo $_{2}$ V $_{2}$ O $_{8}$ in magnetic field perpendicular to the axis which is the chain direction. With applying magnetic field along the axis at 3.5 K, the antiferromagnetic order with the easy axis along the axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the axis. We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in magnetic field is reproduced by the theoretical calculation based on the spin $frac{1}{2}$ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.

論文

Variational wavefunction for the periodic Anderson model with onsite correlation factors

久保勝規; 大西弘明

Journal of the Physical Society of Japan, 86(1), p.013701_1 - 013701_4, 2017/01

https://doi.org/10.7566/JPSJ.86.013701

被引用回数：3 パーセンタイル：21.19(Physics, Multidisciplinary)

We propose a variational wavefunction containing parameters to tune the probabilities of all the possible onsite configurations for the periodic Anderson model. We call it the full onsite-correlation wavefunction (FOWF). This is a simple extension of the Gutzwiller wavefunction (GWF), in which one parameter is included to tune the double occupancy of the electrons at the same site. We compare the energy of the GWF and the FOWF evaluated by the variational Monte Carlo method and that obtained with the density-matrix renormalization group method. We find that the energy is considerably improved in the FOWF. On the other hand, the physical quantities do not change significantly between these two wavefunctions as long as they describe the same phase, such as the paramagnetic phase. From these results, we not only demonstrate the improvement by the FOWF, but we also gain insights on the applicability and limitation of the GWF to the periodic Anderson model.

論文

iBNCT用線形加速器のビームコミッショニング

内藤富士雄*; 穴見昌三*; 池上清*; 魚田雅彦*; 大内利勝*; 大西貴博*; 大場俊幸*; 帯名崇*; 川村真人*; 熊田博明*; et al.

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.1244 - 1246, 2016/11

http://www.pasj.jp/web_publish/pasj2016/proceedings/PDF/TUP1/TUP118.pdf

いばらき中性子医療研究センターのホウ素中性子捕獲療法(iBNCT)システムは線形加速器で加速された8MeVの陽子をBe標的に照射し、中性子を発生させる。この線形加速器システムはイオン源, RFQ, DTL, ビーム輸送系と標的で構成されている。このシステムによる中性子の発生は2015年末に確認されているが、その後システムの安定性とビーム強度を共に高めるため多くの改修を施した。そして本格的なビームコミッショニングを2016年5月中旬から開始する。その作業の進展状況と結果を報告する。

報告書

坑道周辺岩盤の概念再構築に関する研究; 平成26年度(委託研究)

小島圭二*; 大西有三*; 青木謙治*; 杤山修*; 西垣誠*; 登坂博行*; 吉田英一*; 村上裕晃; 笹尾英嗣

JAEA-Research 2015-017, 54 Pages, 2015/12

JAEA-Research-2015-017.pdf:17.3MB

本報告書は、地層処分におけるニアフィールドコンセプトをより現実的に再構築する研究に関するものである。平成27年度は、当委員会の最終年度に当たるため、ニアフィールドコンセプトの再構築に関する検討概要と基本的考え方のまとめを行った。また、委員会での検討事項を整理して、「現実的なニアフィールドコンセプトの再構築」の残された課題を抽出した。特に、「2011年東日本大震災」後に、安全に関する社会のパラダイムが大きくシフトしたことを考慮して、地層処分に関して、社会が従来の安全概念では受け入れがたくなっていると考えられる事項も整理した。また、地下研究施設/ニアフィールド領域で実証可能な、地層処分「必須の重要事項」への対応を検討した。これらを通して、今後の地層処分/ニアフィールド領域の研究開発の方向を示した。

論文

Magnetic excitations of spin nematic state in frustrated ferromagnetic chain

大西弘明

Journal of the Physical Society of Japan, 84(8), p.083702_1 - 083702_4, 2015/08

https://doi.org/10.7566/JPSJ.84.083702

被引用回数：25 パーセンタイル：78.62(Physics, Multidisciplinary)

By exploiting density-matrix renormalization group techniques, we investigate the dynamical spin structure factor of a spin-1/2 Heisenberg chain with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions in an applied magnetic field. In a field-induced spin nematic regime, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-ranged longitudinal and short-ranged transverse spin correlations, respectively. The gapless point coincides with the dominant longitudinal spin correlation, whereas the gap position exhibits a characteristic field dependence contradicting the dominant transverse spin correlation.

論文

Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain

大西弘明

Journal of Physics; Conference Series, 592(1), p.012109_1 - 012109_6, 2015/03

https://doi.org/10.1088/1742-6596/592/1/012109

被引用回数：8 パーセンタイル：91.48(Physics, Atomic, Molecular & Chemical)

By exploiting density-matrix renormalization group techniques, we investigate the spin dynamics of a spin-1/2 one-dimensional $J_{1}$ - $J_{2}$ XXZ model with competing ferromagnetic $J_{1}$ and antiferromagnetic $J_{2}$ under applied magnetic fields. In a high-field phase, the formation of two-magnon bound states leads to a spin quadrupole state, the so-called spin nematic state. The longitudinal spin and quadrupole correlations are quasi-long-ranged, while the transverse spin correlation is short-ranged. Accordingly, the longitudinal component of the spin excitation has a gapless mode, while the transverse component exhibits a gapped mode. The easy-plane anisotropy disfavors the two-magnon bound state, and in contrast the easy-axis anisotropy stabilizes the two-magnon bound state. We will report detailed analyses of the dependence on exchange coupling parameters and magnetic field, and discuss possible relevance to real compounds such as LiCuVO $_{4}$ .

論文

会議報告; The 16th International Workshop on Radiative Properties of Hot Dense Matter会議

佐々木明; 西村博明*; 大西直文*

プラズマ・核融合学会誌, 91(2), p.166 - 167, 2015/02

http://www.jspf.or.jp/Journal/PDF_JSPF/jspf2015_02/jspf2015_02-166.pdf

2014年9月にオーストリア、ウィーンで開催されたThe 16th International Workshop on Radiative Properties of Hot Dense Matter会議の参加報告で、会議において議論された、高温、高密度プラズマ中の原子過程、輻射輸送の研究の現状、今後の課題について議論した。米国リバモア研究所におけるNIF(National Ignition Facility)の現状、XFELを用いた実験などのトピックスについて紹介した。また、衝突輻射モデル計算コード比較ワークショップなどの分野の研究者の活動について紹介した。