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論文

Ferrimagnetic structure in the high-pressure phase of $$alpha$$-Mn

荒木 新吾*; 岩本 凱成*; 秋葉 和人*; 小林 達生*; 宗像 孝司*; 金子 耕士; 長壁 豊隆

Physical Review B, 110(9), p.094420_1 - 094420_7, 2024/09

$$alpha$$-Mn相は、自発磁化が0.02$${mu}_{rm B}$$/Mnと比較的小さいにもかかわらず、圧力誘起弱強磁性(WFM)状態で大きな異常ホール効果(AHE)を示す。このAHEの背後にある根本的な機構を理解するために、2.0GPaの圧力下で単結晶中性子回折測定を行い、WFM相の磁気構造を決定した。I、II、III-1、IV-1位置のMnは、ほぼコリニアーな磁気モーメントが[001]方向に揃ったフェリ磁性構造を持つことを見出した。一方で、III-2とIV-2位置のMnの微小な磁気モーメントは(001)面内を向いている。この磁気構造で計算したネットの磁気モーメントの大きさ(-0.020$${pm}$$0.005)$${mu}_{rm B}$$/Mn原子)は、実験で決定された自発磁化と非常によく一致する。$$q$$ = (0, 0, 0)での磁気反射の観測は、AHEの出現の重要な条件を満たしている。

論文

Singular continuous and nonreciprocal phonons in quasicrystal AlPdMn

松浦 直人*; Zhang, J.*; 上村 祥史*; 古府 麻衣子; 枝川 圭一*

Physical Review Letters, 133(13), p.136101_1 - 136101_5, 2024/09

In quasicrystals lacking translational symmetry but having highly ordered structures, understanding how phonons propagate in their aperiodic lattices remains an unsolved issue. We present an inelastic neutron scattering study on acoustic phonon modes of icosahedral quasicrystal AlPdMn, revealing hierarchical pseudo-gap structure in low-energy acoustic modes. Additionally, phonon intensities are asymmetric in energy and wave vectors with respect to the Bragg peak, indicating characteristic nonreciprocal phonon propagation in quasicrystals.

論文

Antiferromagnetism and phase stability of CrMnFeCoNi high-entropy alloy

Zhu, L.*; He, H.*; Naeem, M.*; Sun, X.*; Qi, J.*; Liu, P.*; Harjo, S.; 中島 健次; Li, B.*; Wang, X.-L.*

Physical Review Letters, 133(12), p.126701_1 - 126701_6, 2024/09

It has long been suspected that magnetism could play a vital role in the phase stability of multi- component high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below $$sim$$80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as $$gamma$$-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the $$langle$$111$$rangle$$ direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.

論文

Dramatic elastic response at the critical end point in UTe$$_2$$

Vali$v{s}$ka, M.*; Haidamak, T.*; Cabala, A.*; Posp$'i$$v{s}$il, J.*; Bastien, G.*; Sechovsk$'y$, V.*; Prokle$v{s}$ka, J.*; 柳澤 達也*; Opletal, P.; 酒井 宏典; et al.

Physical Review Materials (Internet), 8(9), p.094415_1 - 094415_9, 2024/09

Elastic responses at the metamagnetic transition in UTe$$_2$$ are studied at high field. The elastic anomaly becomes the strongest at the critical-end-point. Similar behavior was also observed in another metamagnet UCoAl, suggesting a universal elastic response triggered by critical magnetic fluctuations.

論文

Octupolar edge state in an $$e_g$$ orbital system on a square lattice

久保 勝規

Physical Review B, 110(7), p.075110_1 - 075110_7, 2024/08

A tight-binding model for $$e_g$$ orbitals on a square lattice is investigated. We consider only the nearest-neighbor hopping and the model is characterized by two hopping parameters, $$t_1$$ and $$t_2$$. There are Dirac points in the electronic band structure and the type of the Dirac points (type-I or type-II) depends on the ratio $$t_2/t_1$$. For the case of the type-I Dirac points, edge states appear for a lattice with edges perpendicular to the $$[11]$$ direction. The edge states at a certain momentum along the edges have octupole moments with opposite signs between the right and left edges. Thus, these edge states can be called helical octupolar edge states. This study bridges the research fields of topological phenomena and multipole physics.

論文

Nuclear structure properties of $$^{193-200}$$Hg isotopes within large-scale shell model calculations

Sahoo, S.*; Srivastava, P. C.*; 清水 則孝*; 宇都野 穣

Physical Review C, 110(2), p.024306_1 - 024306_16, 2024/08

G行列をもとにした有効相互作用であるKHEE相互作用を用いて、$$^{193-200}$$Hgの低励起状態の殻模型計算を行った。偶偶核の$$8^+$$$$10^+$$$$12^+$$の励起エネルギーが近いことなど、イラスト状態のエネルギー準位をよく再現した。また、$$2^+$$の電気四重極モーメントが正の値であることも再現し、オブレート変形していることを確かめた。イラスト状態間の$$E2$$遷移が一部強く抑制されているという現象について調べ、配位の変化によるものであることを示した。

論文

Reevaluation of structures in $$^{70}$$Se from combined conversion-electron and $$gamma$$-ray spectroscopy

Smallcombe, J.; Garnsworthy, A. B.*; Korten, W.*; Singh, P.*; Muir, D.*; Pr$'o$chniak, L.*; Ali, F. A.*; Andreoiu, C.*; Ansari, S.*; Ball, G. C.*; et al.

Physical Review C, 110(2), p.024318_1 - 024318_16, 2024/08

In the selenium isotopes various shape phenomena are present, in particular the emergence of a dominant oblate deformation in the most neutron-deficient isotopes has been observed. The scenario of shape coexisting oblate and prolate bands has been proposed across the isotopic chain, with the crossing point of such bands being located near $$^{70}$$Se, where no coexistence has yet been identified. To determine the presence or absence of any low-lying $$0^+$$ state in $$^{70}$$Se, confirm the level structure, and interpret the nuclear deformation with theoretical models. A combined internal conversion electron and $$gamma$$-ray spectroscopy study was undertaken with the SPICE and TIGRESS spectrometers at the TRIUMF-ISAC-II facility. Nuclear models were provided by the Generalised Triaxial Rotor Model (GTRM) and the collective Generalised Bohr Hamiltonian (GBH).Despite a comprehensive search, no evidence was found for the existence of a $$0^+$$ state below 2 MeV in $$^{70}$$Se. Significant discrepancies to the previously established positive parity level scheme were found. GBH calculations using UNEDF1 mass parameters were found to reproduce the revised low-lying level structure well. $$^{70}$$Se does not have a well defined axial shape. The 2$$_2^{+}$$ state at 1601 keV resembles a quasi-$$gamma$$ excitation rather than a member of a shape coexisting band; the presence of such a band is all but ruled out.

論文

Magnonic $$varphi$$ Josephson junctions and synchronized precession

仲田 光樹; Zou, J.*; Klinovaja, J.*; Loss, D.*

Physical Review Research (Internet), 6(3), p.033207_1 - 033207_11, 2024/08

We uncover theoretically that a surprisingly rich dynamics can emerge in magnetic junctions due to intrinsic non-local damping, using analytical and numerical methods. In particular, under microwave pumping, we show that coherent spin precession in the right and left insulating ferromagnet (FM) of the junction becomes synchronized by non-local damping and thereby a magnonic analog of the $$varphi$$ Josephson junction emerges, where $$varphi$$ stands here for the relative precession phase of right and left FM in the stationary limit. Remarkably, $$varphi$$ decreases monotonically from $$ pi$$ to $$pi/2$$ as the magnon-magnon interaction, arising from spin anisotropies, increases. Moreover, we also find a magnonic diode effect giving rise to rectification of magnon currents. Our predictions are readily testable with current device and measurement technologies at room temperatures.

論文

Elastic and inelastic neutron scattering experiments under high pressure in the frustrated antiferromagnet CuFeO$$_{2}$$

寺田 典樹*; Khalyavin, D. D.*; Manuel, P.*; 浅井 晋一郎*; 益田 隆嗣*; 齋藤 開*; 中島 多朗*; 長壁 豊隆

Physical Review B, 110(2), p.024406_1 - 024406_9, 2024/07

フラストレート反強磁性体CuFeO$$_{2}$$は、圧力により、コメンシュレートなコリニアー相(CM1)からいくつかのインコメンシュレートでノンコリニアーな相への複雑な磁気相転移を示す。圧力が磁気相互作用に及ぼす影響を調べるために、高圧下で中性子回折および非弾性中性子散乱実験を行った。圧力が増すと、CM1基底状態は臨界圧力($${P}$$ $$leqq$$ 3GPa)以下でも磁場の印加に対して不安定になる。これは、2.1GPaで臨界磁場$${H_{c1}}$$が7.5Tから4.5Tに大幅に減少したことで確かめられた。さらに、スピン波分散関係のエネルギーギャップは、$$P$$=2.1GPaの圧力印加によって1.0meVから0.88meVに減少する。実験結果をスピン波計算と比較すると、スピン波励起の変化は、一軸異方性項または最近接交換相互作用の分離度のいずれかの減少によって説明できることがわかった。

論文

Theory of the inverse Rashba-Edelstein effect induced by thermal spin injection

細川 海慈*; 山 正樹*; 松尾 衛; 加藤 岳生*

Physical Review B, 110(3), p.035309_1 - 035309_12, 2024/07

Our result provides an important foundation for an accurate analysis of the inverse Rashba-Edelstein effect induced by thermal spin injection.

論文

Lattice dynamics of CH(NH$$_{2}$$)$$_{2}$$PbI$$_{3}$$ and CH(NH$$_{2}$$)$$_{2}$$SnI$$_{3}$$ investigated by inelastic X-ray scattering and comparison of their elastic properties

玉造 博夢; 村上 洋一*; 齋藤 紀子*; 大橋 直樹*; 筒井 智嗣*

Physical Review B, 110(2), p.024301_1 - 024301_8, 2024/07

Using the inelastic X-ray scattering (IXS) technique, we investigate the lattice dynamics of inorganic-organic hybrid iodide perovskites FAPbI$$_{3}$$ and FASnI$$_{3}$$ (FA $$equiv$$ CH(NH$$_{2}$$)$$_{2}$$, formamidinium) in their cubic $$alpha$$ phase and tetragonal $$beta$$ phase. We find that the IXS spectra of FASnI$$_{3}$$ are highly broad at all momentum points, as has been widely observed in the Pb-based halide perovskites. The speeds of sound (phonon group velocities) and absolute values of elastic constants of FASnI$$_{3}$$ are smaller than those of FAPbI$$_{3}$$ in both phases. In addition, no significant difference in the phonon lifetimes of FAPbI$$_{3}$$ and FASnI$$_{3}$$ is observed. These results correlate better with the reported tendency that the lattice thermal conductivity of ASnX$$_{3}$$ is lower than that of APbX$$_{3}$$. We discuss that our results also favor the up-conversion mechanism by acoustic phonons in the phonon bottleneck effect for the long lifetime of hot carriers.

論文

Significance of the refraction effect on the $$p-d$$ elementary process in the ($$p,pd$$) reaction

吉田 数貴; 茶園 亮樹*; 緒方 一介*

Physical Review C, 110(1), p.014617_1 - 014617_9, 2024/07

In the present work, we investigate the deuteron refraction effect in the exclusive ($$p,pd$$) reactions. The refraction effect on the $$p-d$$ elementary process is taken into account by the local semiclassical approximation to the distorted waves. The results are compared with those obtained with the asymptotic momentum approximation, which is standardly applied to the distorted wave impulse approximation framework. It is shown that the refraction effect drastically changes the energy sharing distribution of the $$^{16}$$O($$p,pd$$)$$^{14}$$N reaction at 101.3 MeV and gives a better agreement with experimental data.

論文

Difference in peripherality of the inclusive $$(p, p'x)$$ and $$(d, d'x)$$ reactions and its implications for a phenomenological reaction model

中田 響*; 中山 梓介; 吉田 数貴; 渡辺 幸信*; 緒方 一介*

Physical Review C, 110(1), p.014616_1 - 014616_8, 2024/07

これまでの研究で、$$(n, n'x)$$反応や$$(p, p'x)$$反応の現象論的モデルに表面補正を導入することの重要性が明らかにされ、これらの知見は核データ評価の向上に大きく貢献してきた。しかし、$$(d, d'x)$$反応における表面補正の必要性についてはほとんど研究されていない。本研究では、$$(p, p'x)$$反応と$$(d, d'x)$$反応のエネルギースペクトルとその動径方向分布を1ステップの半古典歪曲波モデルにより計算した。その結果、$$(d,d'x)$$反応のエネルギースペクトルの動径方向分布は$$(p,p'x)$$反応のものに比べて原子核の外側の領域にシフトしていることが分かった。この知見に基づき、$$(d, d'x)$$反応の現象論的モデルに$$(p, p'x)$$反応よりも大きな表面補正を考慮したところ、$$(d, d'x)$$反応スペクトルの実験値をよく再現する計算値が得られた。この結果から、$$(d,d'x)$$反応の表面性は$$(p,p'x)$$反応よりも顕著であること、またそのために$$(d,d'x)$$反応には$$(p,p'x)$$反応よりも強い表面補正を導入すべきであることが分かった。

論文

Dual chiral density wave induced oscillating Casimir effect

藤井 大輔; 中山 勝政*; 鈴木 渓

Physical Review D, 110(1), p.014039_1 - 014039_15, 2024/07

カシミア効果は、微小体積に閉じ込められた光子場から誘起されることが知られており、また、そのフェルミオン的な対応物も、幅広い量子系で予言されている。ここでは、薄い有限密度クォーク物質において、どのような種類のカシミア効果がクォーク場から起こりうるかを調べる。特に、有限密度クォーク物質の基底状態の候補である二重カイラル密度波において、カシミアエネルギーが物質の厚さの関数として振動することを見いだした。この振動するカシミア効果は、Weyl半金属におけるカシミア効果と類似しており、クォーク場の運動量空間におけるWeyl点に起因すると考えることができる。さらに、クォークのフェルミ海からも振動が誘起され、全カシミアエネルギーは複数の振動の重ね合わせから構成されることを示す。

論文

Spin and lattice dynamics in the van der Waals antiferromagnet MnPSe$$_{3}$$

Liao, J.*; Huang, Z.*; Shangguan, Y.*; Zhang, B.*; Cheng, S.*; Xu, H.*; 梶本 亮一; 蒲沢 和也*; Bao, S.*; Wen, J.*

Physical Review B, 109(22), p.224411_1 - 224411_10, 2024/06

Antiferromagnetic van der Waals family $$M$$P$$X_{3}$$ ($$M$$ = Fe, Mn, Co, and Ni; $$X$$ = S and Se) have attracted significant research attention due to the possibility of realizing long-range magnetic order down to the monolayer limit. Here, we perform inelastic neutron scattering measurements on single-crystal samples of MnPSe$$_{3}$$, a member of the $$M$$P$$X_{3}$$ family, to study the spin dynamics and determine the effective spin model. The excited magnon bands are well characterized by a spin model, which includes a Heisenberg term with three intraplane exchange parameters ($$J_{1} = -0.73$$ meV, $$J_{2} = -0.014$$ meV, $$J_{3} = -0.43$$ meV) and one interplane parameter ($$J_{c} = -0.054$$ meV), and an easy-plane single-ion anisotropy term ($$D = -0.035$$ meV). Additionally, we observe the intersection of the magnon and phonon bands but no anomalous spectral features induced by the formation of magnon-phonon hybrid excitations at the intersecting region. We discuss possible reasons for the absence of such hybrid excitations in MnPSe$$_{3}$$.

論文

Large-scale shell model study of $$beta^-$$decay properties of $$N$$ = 126, 125 nuclei; Role of Gamow-Teller and first-forbidden transitions in the half-lives

Kumar, A.*; 清水 則孝*; 宇都野 穣; Yuan, C.*; Srivastava, P. C.*

Physical Review C, 109(6), p.064319_1 - 064319_18, 2024/06

極めて中性子の多い、中性子数126、125原子核の半減期はr過程元素合成の第3ピークに大きな影響を与えることが知られているが、その測定は未だに限られている。本研究ではこれらの半減期を大規模殻模型計算によって求めた。G行列をもとにしたKHHE相互作用を用い、ガモフテラー遷移と第一禁止遷移による半減期を系統的に得た。安定核近傍の実験値をよく再現することを確かめた。安定核付近では陽子が$$h_{11/2}$$軌道を多く占めているために、ガモフテラー遷移が強く抑制されるが、陽子数の減少とともにその寄与が主になることを予言した。

論文

Acoustomagnonic spin Hall effect in honeycomb antiferromagnets

佐野 涼太郎*; 大湊 友也*; 松尾 衛

Physical Review Letters, 132(23), p.236302_1 - 236302_9, 2024/06

We propose an ac intrinsic magnon spin Hall current driven by surface acoustic waves as a novel probe for such antiferromagnets. Our results pave the way towards mechanical detection and manipulation of the magnetic order in two-dimensional antiferromagnets.

論文

Chirality-induced phonon-spin conversion at an interface

船戸 匠*; 松尾 衛; 加藤 岳生*

Physical Review Letters, 132(23), p.236201_1 - 236201_7, 2024/06

Our results clearly illustrate the microscopic origin of spin current generation by chiral phonons and may lead to a breakthrough in the development of spintronic devices without heavy elements.

論文

Nuclear quantum effect on the elasticity of ice VII under pressure; A Path-integral molecular dynamics study

土屋 旬*; 志賀 基之; 常行 真司*; Thompson, E. C.*

Physical Review Research (Internet), 6(2), p.023302_1 - 023302_6, 2024/06

第一原理経路積分分子動力学計算を用いて、水素原子の核量子効果が高圧・常温条件下での氷VIIの弾性に及ぼす影響を調べた。その結果、40GPa以上の圧力において、氷VIIの静的無秩序構造から動的無秩序構造への転移に対して核量子効果が寄与していることがわかった。この転移は弾性定数の不連続な増加によって特徴づけられる。第一原理分子動力学計算と第一原理経路積分分子動力学計算の比較から、核量子効果によって70GPa, 300Kにおける氷の弾性定数が約20%増加することが明らかになった。

論文

Single helicity of the triple-$$q$$ triangular skyrmion lattice state in the cubic chiral helimagnet EuPtSi

松村 武*; 田端 千紘; 金子 耕士; 中尾 裕則*; 垣花 将司*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Physical Review B, 109(17), p.174437_1 - 174437_8, 2024/05

We investigated the magnetic helicity of the triple-$$q$$ magnetic structure of the triangular skyrmion lattice in the A-phase of EuPtSi for a magnetic field along the [111] axis by resonant X-ray diffraction using a circularly polarized beam. We show that all three Fourier components of the triple-$$q$$ structure are perpendicular to the respective $$q$$ vectors and have the same helicity. They are connected by the rotation operations about the [111] axis. The helicity is the same as that of the single-$$q$$ helimagnetic phase at low fields, suggesting that the antisymmetric exchange interaction inherent in the chiral structure supports the formation of the triangular skyrmion lattice. We also observe that the helical plane in the helimagnetic phase is tilted to the magnetic field to form a conical structure before the first-order transition to the skyrmion lattice phase.

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