検索対象:     
報告書番号:
※ 半角英数字
 年 ~ 
 年
検索結果: 102 件中 1件目~20件目を表示

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 ...

発表言語

Initialising ...

発行年

Initialising ...

開催年

Initialising ...

選択した検索結果をダウンロード

論文

Quasi-fractionalization of edge spin in chirality-assisted cluster-based Haldane state on triangular spin tube

杉本 貴則*; 遠山 貴己

Communications Physics (Internet), 6, p.291_1 - 291_6, 2023/10

 被引用回数:2 パーセンタイル:23.32(Physics, Multidisciplinary)

Fractionalization of quantum degrees of freedom holds the key to finding new phenomena in physics, e.g., the quark model in hadron physics and the spin-charge separation in strongly-correlated electron systems. A typical example of the fractionalization in quantum spin systems is the spin-1 Haldane state, whose intriguing characteristics are well described by fractionalized virtual spins, delivering two individual spin-1/2 degrees of freedom as edge states. Here we theoretically propose an exotic extension of the Haldane state to the pseudo spin-1 model consisting of the mixture of real spin and spin chirality, resulting in quasi-fractionalization of spin-1/2 magnetization, i.e., an approximately-1/4 spin. Existence of the edge state is confirmed both analytically and numerically in a triangular spin tube, combining a low-energy perturbation theory and variational matrix-product state method. Our study not only proposes an unconventional quantum spin object but paves a way to chop the elementary quantities further.

論文

Confined states and topological phases in two-dimensional quasicrystalline $$pi$$-flux model

Ghadimi, R.*; Hori, Masahiro*; 杉本 貴則*; 遠山 貴己

Physical Review B, 108(12), p.125104_1 - 125104_18, 2023/09

 被引用回数:5 パーセンタイル:58.52(Materials Science, Multidisciplinary)

Motivated by topological equivalence between an extended Haldane model and a chiral-$$pi$$-flux model on a square lattice, we apply $$pi$$-flux models to two-dimensional bipartite quasicrystals with rhombus tiles in order to investigate topological properties in aperiodic systems. Topologically trivial $$pi$$-flux models in the Ammann-Beenker tiling lead to massively degenerate confined states whose energies and fractions differ from the zero-flux model. This is different from the $$pi$$-flux models in the Penrose tiling, where confined states only appear at the center of the bands as is the case of a zero-flux model. Additionally, Dirac cones appear in a certain $$pi$$-flux model of the Ammann-Beenker approximant, which remains even if the size of the approximant increases. Nontrivial topological states with nonzero Bott index are found when staggered tile-dependent hoppings are introduced in the $$pi$$-flux models. This finding suggests a direction in realizing nontrivial topological states without a uniform magnetic field in aperiodic systems.

論文

Higher-dimensional Hofstadter butterfly on the Penrose lattice

Ghadimi, R.*; 杉本 貴則*; 遠山 貴己

Physical Review B, 106(20), p.L201113_1 - L201113_6, 2022/11

 被引用回数:5 パーセンタイル:42.27(Materials Science, Multidisciplinary)

It is now possible to use quasicrystals to search for novel topological phenomena enhanced by their peculiar structure characterized by an irrational number and high-dimensional primitive vectors. Here, we extend the concept of a topological insulator with an emerging staggered local magnetic flux (i.e., without external fields), similar to Haldane's honeycomb model, to the Penrose lattice as a quasicrystal. The Penrose lattice consists of two different tiles, where the ratio of the numbers of tiles corresponds to an irrational number. Contrary to periodic lattices, the periodicity of the energy spectrum with respect to the magnetic flux no longer exists, reflecting the irrational number in the Penrose lattice. Calculating the Bott index as a topological invariant, we find topological phases appearing in a fractal energy spectrum similar to the Hofstadter butterfly. More intriguingly, by folding the one-dimensional aperiodic magnetic flux into a two-dimensional periodic flux space, the fractal structure of the energy spectrum is extended to a higher dimension, whose section corresponds to the Hofstadter butterfly.

論文

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

山本 風海; 金正 倫計; 林 直樹; Saha, P. K.; 田村 文彦; 山本 昌亘; 谷 教夫; 高柳 智弘; 神谷 潤一郎; 菖蒲田 義博; et al.

Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09

 被引用回数:7 パーセンタイル:74.40(Nuclear Science & Technology)

J-PARC 3GeVシンクロトロン(RCS)は、最大1MWの大強度ビームを25Hzという早い繰り返しで中性子実験及び下流の主リングシンクロトロンに供給することを目的に設計された。2007年の加速器調整運転開始以降、RCSではビーム試験を通じて加速器の設計性能が満たされているかの確認を進め、必要に応じてより安定に運転するための改善を行ってきた。その結果として、近年RCSは1MWのビーム出力で連続運転を行うことが可能となり、共用運転に向けた最後の課題の抽出と対策の検討が進められている。本論文ではRCSの設計方針と実際の性能、および改善点について議論する。

論文

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

 被引用回数:4 パーセンタイル:40.86(Materials Science, Multidisciplinary)

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。

論文

Topological superconductivity in quasicrystals

Ghadimi, R.*; 杉本 貴則*; 田中 佳織*; 遠山 貴己

Physical Review B, 104(14), p.144511_1 - 144511_10, 2021/10

 被引用回数:30 パーセンタイル:87.03(Materials Science, Multidisciplinary)

We propose realization of non-Abelian topological superconductivity in two-dimensional quasicrystals by the same mechanism as in crystalline counterparts. Specifically, we study a two-dimensional electron gas in Penrose and Ammann-Beenker quasicrystals with Rashba spin-orbit coupling, perpendicular Zeeman magnetic field, and conventional $$s$$-wave superconductivity. We find that topological superconductivity with broken time-reversal symmetry is realized in both Penrose and Ammann-Beenker quasicrystals at low filling, where the Bott index is unity. The topological nature of this phase is confirmed by the existence of a zero-energy surface bound state and the chiral propagation of a wave packet projected onto the midgap bound state along the surfaces. Furthermore, we confirm the existence of a single Majorana zero mode each in a vortex at the center of the system and along the surfaces, signifying the non-Abelian character of the system when the Bott index is unity.

論文

Coexistence of strong and weak Majorana zero modes in an anisotropic XY spin chain with second-neighbor interactions

Wada, Kazuhiro*; 杉本 貴則*; 遠山 貴己

Physical Review B, 104(7), p.075119_1 - 075119_12, 2021/08

 被引用回数:7 パーセンタイル:42.22(Materials Science, Multidisciplinary)

We theoretically investigate Majorana zero modes emerging in an anisotropic XY spin chain with second-neighbor interactions. The spin chain is mathematically equivalent to the Kitaev chain comprised of spinless fermions if only nearest-neighbor interactions are considered. Recent studies on the Kitaev chain with long-ranged interactions, have presented coexistence of several Majorana zero modes. Investigating the topological phase diagram of the anisotropic XY spin chain with second-neighbor interactions, we find coexistence of several Majorana zero modes similar to the Kitaev chain. However, we confirm that one of the zero modes is restricted into a Hilbert subspace. The mode is regarded as a so-called weak zero mode that should exhibit thermodynamical properties different from a (strong) zero mode appearing in the whole Hilbert space. Since the quantum statistics of spin is the same as a hard-core boson, we expect an experimental realization of the weak mode in not only quantum spin materials but also optical lattices for cold atom systems.

論文

Mean-field study of the Bose-Hubbard model in the Penrose lattice

Ghadimi, R.*; 杉本 貴則*; 遠山 貴己

Physical Review B, 102(22), p.224201_1 - 224201_9, 2020/12

 被引用回数:14 パーセンタイル:59.14(Materials Science, Multidisciplinary)

We examine the Bose-Hubbard model in the Penrose lattice based on inhomogeneous mean-field theory. Since the averaged coordination number in the Penrose lattice is four, the mean-field phase diagram consisting of the Mott insulator (MI) and superfluid (SF) phase is similar to that of the square lattice. However, the spatial distribution of the Bose condensate in the SF phase is significantly different from uniform distribution in the square lattice. We find a fractal structure in its distribution near the MI-SF phase boundary. The emergence of the fractal structure is a consequence of the cooperative effect between quasiperiodicity in the Penrose lattice and criticality at the phase transition.

論文

Atomistic modeling of hardening in spinodally-decomposed Fe-Cr binary alloys

鈴土 知明; 高見澤 悠; 西山 裕孝; Caro, A.*; 外山 健*; 永井 康介*

Journal of Nuclear Materials, 540, p.152306_1 - 152306_10, 2020/11

 被引用回数:12 パーセンタイル:75.34(Materials Science, Multidisciplinary)

熱時効したFe-Cr合金はスピノーダル分解によって硬化を引き起こし、これはいわゆる475C脆性の直接的な原因である。スピノーダル分解が原子的相互作用によってどのように硬化を引き起こすのかを示すため、数値シミュレーションと実験を実施した。数値的な結果では、硬さが短距離秩序(SRO)パラメーターと比例することを示され、実験でもこの関係を統計誤差内で再現した。どちらの結果も、隣接するCr-Cr原子ペアが本質的に硬化を引き起こすことを示唆した。なぜなら、SROがそのようなペアの出現確率に一意的に依存しているからである。硬化の主な原因がそのようなCr-Crペア付近を通過する転位のピン止め効果であることが示唆されたが、このアイデアはさらなるモデリング研究により裏付けられた。

論文

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, p.3429_1 - 3429_7, 2020/07

 被引用回数:51 パーセンタイル:92.31(Multidisciplinary Sciences)

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, KCu$$_6$$AlBiO$$_4$$(SO$$_4$$)$$_5$$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.

論文

Dynamical density matrix renormalization group study of spin and charge excitations in the four-leg $$t$$-$$t'$$-$$J$$

遠山 貴己; 森 道康; 曽田 繁利*

Physical Review B, 97(23), p.235137_1 - 235137_7, 2018/06

AA2018-0171.pdf:1.43MB

 被引用回数:12 パーセンタイル:46.67(Materials Science, Multidisciplinary)

We investigate the dynamical spin and charge structure factors of the $$t$$-$$t'$$-$$J$$ four-leg ladder by using dynamical density-matrix renormalization group. The dynamical charge structure factor along the momentum direction from $$q=(0,0)$$ to $$(pi,0)$$ clearly shows low-energy excitations corresponding to the stripe order in hole doping. On the other hand, the stripe order weakens in electron doping, resulting in less low-energy excitations in the charge channel. In spin channel, we find incommensurate spin excitations near $$q=(pi,pi)$$ forming a hour-glass behavior in hole doping, while in electron doping we find clearly spin-wave-like dispersions starting from $$q=(pi,pi)$$. Along the $$(0,0)$$-$$(pi,0)$$ direction, the spin excitations are strongly influenced by the stripes in hole doping, resulting in two branches that form a discontinuous behavior in the dispersion. In contrast, the electron-doped systems show a downward shift in energy toward $$(pi,0)$$.

論文

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

 被引用回数:6 パーセンタイル:26.66(Materials Science, Multidisciplinary)

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.

論文

Observation of momentum-dependent charge excitations in hole-doped cuprates using resonant inelastic X-ray scattering at the oxygen $$K$$ edge

石井 賢司*; 遠山 貴巳*; 浅野 駿*; 佐藤 研太朗*; 藤田 全基*; 脇本 秀一; 筒井 健二*; 曽田 繁利*; 宮脇 淳*; 丹羽 秀治*; et al.

Physical Review B, 96(11), p.115148_1 - 115148_8, 2017/09

AA2017-0402.pdf:0.81MB

 被引用回数:33 パーセンタイル:77.62(Materials Science, Multidisciplinary)

We investigate electronic excitations in La$$_{2-x}$$(Br,Sr)$$_x$$CuO$$_4$$ using resonant inelastic X-ray scattering (RIXS) at the oxygen $$K$$ edge. We observed momentum-dependent spectral weight below 1 eV, which is consistent with theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model. Our results confirm that the momentum-dependent charge excitations exist on the order of the transfer energy ($$t$$), and the broad spectral line shape indicates damped and incoherent character of the charge excitations at the energy range in the doped Mott insulators.

論文

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

 被引用回数:3 パーセンタイル:13.48(Physics, Applied)

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.

論文

Quasi-spin correlations in a frustrated quantum spin ladder

杉本 貴則*; 森 道康; 遠山 貴巳*; 前川 禎通

Physics Procedia, 75, p.861 - 867, 2015/12

 被引用回数:0 パーセンタイル:0.00(Physics, Applied)

The quasi-spin correlations in a frustrated quantum spin ladder with one-half magnetization are theoretically studied by using the density-matrix renormalization-group method and the quasi- spin transformation. In this model, the frustration induces a gapless-to-gapful phase transition with a strong rung coupling. The gapful state is observed as the one-half magnetization plateau in the magnetization curve. In the magnetization-plateau state, we find that the quasi-spin dimer has a large expectation value with long-ranged correlations. This result does not only comes in useful to clarify the magnetization-plateau state, but gives a crucial information to understand the magnetization curve of the real compound BiCu$$_{2}$$PO$$_{6}$$, whose effective spin model corresponds to ours.

論文

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

 被引用回数:2 パーセンタイル:9.02(Materials Science, Multidisciplinary)

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。

論文

Lifshitz transition induced by magnetic field in frustrated two-leg spin-ladder systems

杉本 貴則*; 森 道康; 遠山 貴巳*; 前川 禎通

JPS Conference Proceedings (Internet), 8, p.034005_1 - 034005_6, 2015/09

The magnetization curve in a frustrated two-leg spin-ladder system is theoretically studied using both analytical and numerical methods. This spin system is mapped onto a hard-core boson system, which is composed of bond-operators describing the triplon excitation. By the analytical method using the mean-field theory on the bond-operators, we show that cusp singularities emerge in the magnetization curve as a function of a magnetic field due to the strong frustration. This originates from a change of number of Fermi points in the bosonic dispersion relation with the applied field. It is analogous to Lifshitz transition. This singularity is clarified by numerical calculation with the density-matrix renormalization-group method. Our results will be useful to understand the magnetization process observed in the frustrated two-leg spin-ladder compound BiCuH$$_{2}$$OPOH$$_{6}$$O.

論文

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

 被引用回数:11 パーセンタイル:42.43(Materials Science, Multidisciplinary)

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 BiCu$$_{2}$$PO$$_{6}$$.

論文

Enhanced charge excitations in electron-doped cuprates by resonant inelastic X-ray scattering

遠山 貴巳*; 筒井 健二; 森 道康; 曽田 繁利*; 柚木 清司*

Physical Review B, 92(1), p.014515_1 - 014515_8, 2015/07

 被引用回数:14 パーセンタイル:49.75(Materials Science, Multidisciplinary)

銅L吸収端共鳴非弾性X線散乱は銅酸化物高温超伝導物質の電荷励起を調べる強力な手法である。この散乱手法による電荷の集団励起の観測可能性を理論的に調べる。散乱プロセスにおける中間状態を経ることで必然的に電子ドープ系の電荷集団励起モードの強度がホールドープ系よりも強くなる。この電子・ホール非対称性は動的電荷構造因子にも現れる。特に電子ドープ系において低運動量変化の低エネルギー領域に新たな増強された励起モードとして現れる。これらの結果は電子ドープ系の新しい電荷励起モードの共鳴非弾性X線散乱による観測可能性を示している。

論文

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

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。

102 件中 1件目~20件目を表示