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論文

Continuum excitations in a spin supersolid on a triangular lattice

Zhu, M.*; Romerio, V.*; Steiger, N.*; Nabi, S. D.*; 村井直樹; 河村聖子; Povarov, K. Y.*; Skourski, Y.*; Sibille, R.*; Keller, L.*; et al.

Physical Review Letters, 133(18), p.186704_1 - 186704_6, 2024/11

https://doi.org/10.1103/PhysRevLett.133.186704

被引用回数：9 パーセンタイル：91.73(Physics, Multidisciplinary)

Magnetic, thermodynamic, neutron diffraction and inelastic neutron scattering are used to study spin correlations in the easy-axis XXZ triangular lattice magnet K $_{2}$ Co(SeO $_{3}$ ) $_{2}$ . Despite the presence of quasi-2D supersolid magnetic order, the low-energy excitation spectrum contains no sharp modes and is instead a broad and structured multiparticle continuum. Applying a weak magnetic field drives the system into an m = 1/3 fractional magnetization plateau phase and restores sharp spin wave modes. To some extent, the behavior at zero field can be understood in terms of spin wave decay. However, the presence of clear excitation minima at the M points of the Brillouin zone suggest that the spinon language may provide a more adequate description, and signals a possible proximity to a Dirac spin liquid state.

論文

Neutron flux and energy resolution of direct-geometry disk-chopper spectrometer AMATERAS at J-PARC

楡井真実; 古府麻衣子; 中島健次; 菊地龍弥*; 河村聖子; 村井直樹; 原田正英; 稲村泰弘

Journal of Neutron Research, 26(2-3), p.75 - 82, 2024/09

https://doi.org/10.3233/JNR-230013

We investigated neutron flux at a sample position and energy resolution of a direct-geometry disk-chopper spectrometer AMATERAS under various chopper conditions and compared them with simulations and calculations. The measured flux was comparable to other similar spectrometers with high flux. The resolution when using a pulse-shaping chopper was in close agreement with the analytical calculations, including the thickness of the disk chopper, the sample size, and the penetration depth into the detector. It is found that the chopper, placed at the intermediate distance of the primary spectrometer, works as a pulse shaper that optimizes the flux and resolution below the incident energy of 10 meV.

論文

Signatures of Kitaev interactions in the van der Waals ferromagnet VI $_{3}$

Gu, Y. Q.*; Gu, Y. M.*; Liu, F.*; 河村聖子; 村井直樹; Zhao, J.*

Physical Review Letters, 132(24), p.246702_1 - 246702_7, 2024/06

https://doi.org/10.1103/PhysRevLett.132.246702

被引用回数：2 パーセンタイル：64.46(Physics, Multidisciplinary)

Materials manifesting the Kitaev model, characterized by bond-dependent interactions on a honeycomb lattice, can host exotic phenomena like quantum spin liquid states and topological magnetic excitations. However, finding such materials remains a formidable challenge. Here, we report high-resolution inelastic neutron scattering measurements performed on VI $_{3}$ , a van der Waals ferromagnetic Mott insulator, covering a wide range of reciprocal space. Our measurements unveil highly anisotropic magnetic excitations in momentum space. Through a comprehensive comparative analysis of various models that incorporate diverse symmetry-allowed magnetic interactions, we find the observed excitations are well captured by a model with a large bond-dependent Kitaev interaction. These results not only help to understand the intriguing properties of VI $_{3}$ , such as the pronounced anomalous thermal Hall effects and strong pressure or structure dependence of magnetism, but also open a new avenue for exploring Kitaev physics.

論文

Excitation spectrum and spin Hamiltonian of the frustrated quantum Ising magnet Pr $_{3}$ BWO $_{9}$

Nagl, J.*; Flavin, D.*; Hayashida, S.*; Povarov, K. Y.*; Yan, M.*; 村井直樹; 河村聖子; Simutis, F.*; Hicken, T. J.*; Luetkens, H.*; et al.

Physical Review Research (Internet), 6(2), p.023267_1 - 023267_18, 2024/06

https://doi.org/10.1103/PhysRevResearch.6.023267

We investigate the rare-earth-based frustrated quantum antiferromagnet Pr $_{3}$ BWO $_{9}$ , previously considered a spin-liquid candidate. Our experimental and theoretical analysis reveals that its ground state is better described as a quantum paramagnet, governed by an Ising model in a transverse field. While in-plane correlations exist, the dominant interactions form frustrated triangular spin tubes via competing ferro-antiferromagnetic bonds. The system's thermodynamic and dynamic properties are significantly influenced by hyperfine interactions and weak structural disorder.

論文

Magnetic boson peak in classical spin glasses

古府麻衣子; 河村聖子; 村井直樹; 石井梨恵子*; 平井大悟郎*; 有馬寛*; 舟越賢一*

Physical Review Research (Internet), 6(1), p.013006_1 - 013006_9, 2024/01

https://doi.org/10.1103/PhysRevResearch.6.013006

We revisited spin dynamics in archetypical classical spin glass systems, such as Cu $_{1-x}$ Mn $_{x}$ (, 0.034, and 0.067) dilute alloys and iron aluminosilicate glass using a modern neutron scattering spectrometer with high neutron flux. The former is crystalline, and the latter is amorphous, where their spin glass state is well separated from magnetically ordered phases. Bose-scaled localized magnetic excitations were observed in both compounds below the spin-freezing temperature ( $T_{rm f}$ ). The spectrum exhibits a maximum at low energy and a broad tail on the high-energy side. The excitation energy tends to be higher for the material with a higher $T_{rm f}$ . Above the $T_{rm f}$ , the spectrum considerably changes with temperature, thereby indicating the emergence of the magnetic relaxation process. The magnetic excitation in the spin glass state has much in common with the boson peak in structural glasses. We consider that the Bose-scaled broad excitation peak is an elementary excitation inherent in disordered systems.

論文

A One-third magnetization plateau phase as evidence for the Kitaev interaction in a honeycomb-lattice antiferromagnet

Shangguan, Y.*; Bao, S.*; Dong, Z.-Y.*; Xi, N.*; Gao, Y.-P.*; Ma, Z.*; Wang, W.*; Qi, Z.*; Zhang, S.*; Huang, Z.*; et al.

Nature Physics, 19(12), p.1883 - 1889, 2023/09

https://doi.org/10.1038/s41567-023-02212-2

被引用回数：19 パーセンタイル：93.50(Physics, Multidisciplinary)

The magnetization of a quantum magnet can be pinned at a fraction of its saturated value by collective effects. One example of such a plateau phase is found in spin-1/2 triangular-lattice antiferromagnets. They feature strong geometrical frustration and the plateau phase therein is often interpreted as arising from an order-by-disorder mechanism driven by quantum fluctuations. Here we observe a one-third magnetization plateau under an applied magnetic field in the spin-1 antiferromagnet Na $_{3}$ Ni $_{2}$ BiO $_{6}$ with a honeycomb lattice, which, with conventional magnetic interactions, would not be geometrically frustrated. Based on our elastic neutron scattering measurements, we propose the spin structure of the plateau phase to be an unusual partial spin-flop ferrimagnetic order. Our theoretical calculations indicate that bond-anisotropic Kitaev interactions are the source of frustration that produces the plateau. These results suggest that Kitaev interactions provide a different route to frustration and phases driven by quantum fluctuations in high-spin magnets.

論文

Spin gap in the weakly interacting quantum spin chain antiferromagnet KCuPO $_{4}$ H $_{2}$ O

藤原理賀; 萩原雅人; 森田克洋*; 村井直樹; 幸田章宏*; 岡部博孝*; 満田節生*

Physical Review B, 107(5), p.054435_1 - 054435_8, 2023/02

https://doi.org/10.1103/PhysRevB.107.054435

被引用回数：3 パーセンタイル：37.63(Materials Science, Multidisciplinary)

= 1/2ハイゼンベルグ直線鎖反強磁性体は、最も単純なスピンモデルであるが、様々な量子多体現象のプラットフォームを提供する。この論文では、準一次元反強磁性体KCuPO $_{4}$ H $_{2}$ Oの磁性を報告した。 $T_{rm{N}}$ = 11.7(1)Kにおいて、格子整合な長距離反強磁性秩序が形成され、その磁気モーメントの大きさは0.31(1) $mu_{rm{B}}$ である事がわかった。また鎖内相互作用と鎖間相互作用の大きさはそれぞれ172Kと4.25(4)Kと見積もられ、/の比は0.0247(3)である。中性子非弾性散乱実験により、 $T_{rm{N}}$ より高温では、一次元ハイゼンベルグ量子スピン鎖の特徴である連続体励起スペクトルが観測され、 $T_{rm{N}}$ より低温では、分散励起にスピンギャップが観測された。これらの結果は、弱く結合した = 1/2ハイゼンベルグスピン鎖系で観測される性質と一致する。

論文

Experimental evidence for the significance of optical phonons in thermal transport of tin monosulfide

Wu, P.*; 村井直樹; Li, T.*; 梶本亮一; 中村充孝; 古府麻衣子; 中島健次; Xia, K.*; Peng, K.*; Zhang, Y.*; et al.

New Journal of Physics (Internet), 25(1), p.013032_1 - 013032_11, 2023/01

https://doi.org/10.1088/1367-2630/acb3ed

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

The understanding of the lattice dynamics is essential for engineering the thermal transport properties in quantum materials. Based on the canonical point of view, acoustic phonons are believed to be the principal thermal carriers in heat flow. Here, in this work, optical phonons are elucidated to play a pivotal role in determining the lattice thermal conductivity in thermoelectric material SnS by using the state-of-the-art inelastic neutron scattering technique combined with first-principles calculations. Additionally, in contrast to acoustic phonons, optical phonons are observed to exhibit pronounced softening and broadening with temperature. Our observations not only shed light on the significance of the optical phonons in thermal transport but also provide a vital clue to suppress the propagation of optical phonons to optimize the thermoelectric performance of SnS.

論文

Partial breakdown of translation symmetry at a structural quantum critical point associated with a ferroelectric soft mode

石井悠衣*; 山本有梨沙*; 佐藤直大*; 南部雄亮*; 河村聖子; 村井直樹; 尾原幸治*; 河口彰吾*; 森孝雄*; 森茂生*

Physical Review B, 106(13), p.134111_1 - 134111_7, 2022/10

https://doi.org/10.1103/PhysRevB.106.134111

被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

We report that complete suppression of a phonon-driven structural phase transition causes partial breakdown of a three-dimensional translation symmetry in a well-defined sublattice. This state is revealed for a dielectric compound, Ba $_{1-x}$ SrAlO, that comprises an AlO network incorporated into a hexagonal Ba(Sr) sublattice. Pair distribution function analyses and inelastic neutron scattering experiments provide clear-cut evidence of the AlO network forming a continuum of Al-O short-range correlations similar to glasses, whereas the Ba(Sr) sublattice preserves the original translational symmetry. This glassy network significantly dampens the phonon spectrum and transforms it into the broad one resembling those typically observed in glass materials.

論文

Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe $_{3}$

Chen, L.*; Mao, C.*; Chung, J.-H.*; Stone, M. B.*; Kolesnikov, A. I.*; Wang, X.*; 村井直樹; Gao, B.*; Delaire, O.*; Dai, P.*

Nature Communications (Internet), 13, p.4037_1 - 4037_7, 2022/07

https://doi.org/10.1038/s41467-022-31612-w

被引用回数：22 パーセンタイル：81.53(Multidisciplinary Sciences)

Spin and lattice are two fundamental degrees of freedom in a solid, and their fluctuations about the equilibrium values in a magnetic ordered crystalline lattice form quasiparticles termed magnons (spin waves) and phonons (lattice waves), respectively. In most materials with strong spin-lattice coupling (SLC), the interaction of spin and lattice induces energy gaps in the spin wave dispersion at the nominal intersections of magnon and phonon modes. Here we use neutron scattering to show that in the two-dimensional (2D) van der Waals honeycomb lattice ferromagnetic CrGeTe $_{3}$ , spin waves propagating within the 2D plane exhibit an anomalous dispersion, damping, and breakdown of quasiparticle conservation, while magnons along the c axis behave as expected for a local moment ferromagnet. These results indicate the presence of dynamical SLC arising from the zero-temperature quantum fluctuations in CrGeTe $_{3}$ , suggesting that the observed in-plane spin waves are mixed spin and lattice quasiparticles fundamentally different from pure magnons and phonons.

論文

Recent update of AMATERAS; A Cold-neutron disk-chopper spectrometer

中島健次; 河村聖子; 古府麻衣子; 村井直樹; 稲村泰弘; 菊地龍弥*; 若井大介*

JPS Conference Proceedings (Internet), 33, p.011089_1 - 011089_7, 2021/03

https://doi.org/10.7566/JPSCP.33.011089

J-PARCに設置されている冷中性子ディスクチョッパー型分光器AMATERASの近況について報告する。最後に報告を行った2017年以降、新たな検出器の増設、散乱真空槽の真空系の更新作業(継続中)等を行っている。また、分解能について再調査を実施した。この他、2018年、2019年のJ-PARCの1MW試験時に試験測定も行った。今後の高度化計画についても触れる。

論文

Field-tuned magnetic structure and phase diagram of the honeycomb magnet YbCl

Hao, Y. Q.*; Wo, H. L.*; Gu, Y. M.*; Zhang, X. W.*; Gu, Y. Q.*; Zheng, S. Y.*; Zhao, Y.*; Xu, G. Y.*; Lynn, J. W.*; 中島健次; et al.

Science China; Physics, Mechanics & Astronomy, 64(3), p.237411_1 - 237411_6, 2021/03

https://doi.org/10.1007/s11433-020-1626-3

被引用回数：12 パーセンタイル：69.00(Physics, Multidisciplinary)

We report thermodynamic and neutron diffraction measurements on the magnetic ordering properties of the honeycomb lattice magnet YbCl. We find YbCl exhibits a Nel type long-range magnetic order at the wavevector (0, 0, 0) below T = 600 mK. This magnetic order is associated with a small sharp peak in heat capacity and most magnetic entropy release occurs above the magnetic ordering temperature. The magnetic moment lies in-plane, parallel to the monoclinic a-axis, whose magnitude m $_{rm Yb}$ = 0.86(3) is considerably smaller than the expected fully ordered moment of 2.24 for the doublet crystal-field ground state. The magnetic ordering moment gradually increases with increasing magnetic field perpendicular to the ab-plane, reaching a maximum value of 1.6(2) at 4 T, before it is completely suppressed above 9 T. These results indicate the presence of strong quantum fluctuations in YbCl.

論文

=0 long-range magnetic order in centennialite CaCu $_{3}$ (OD) $_{6}$ Cl $_{2}$ 0.6D $_{2}$ O; A Spin- $frac{1}{2}$ perfect kagome antiferromagnet with $J_{1}$ - $J_{2}$ - $J_{d}$

飯田一樹*; 吉田紘行*; 中尾朗子*; Jeschke, H. O.*; Iqbal, Y.*; 中島健次; 河村聖子; 宗像孝司*; 稲村泰弘; 村井直樹; et al.

Physical Review B, 101(22), p.220408_1 - 220408_6, 2020/06

https://doi.org/10.1103/PhysRevB.101.220408

被引用回数：28 パーセンタイル：79.78(Materials Science, Multidisciplinary)

鉱物センテニアライトCaCu $_{3}$ (OD) $_{6}$ Cl $_{2}$ 0.6D $_{2}$ Oの結晶構造と磁気構造をシンクロトロンX線回折と中性子回折測定に密度汎関数理論(DFT)と疑似フェルミオン汎関数繰り込み群(PFFRG)の計算を組み合わせることで調べた。CaCu $_{3}$ (OD) $_{6}$ Cl $_{2}$ 0.6D $_{2}$ OではCu $^{2+}$ イオンは反強磁性 $J_{1}$ と幾何学的に完全なカゴメネットワークを形成する。Cu $^{2+}$ とCa $^{2+}$ イオン間のサイト間無秩序は見つからなかった。CaCu $_{3}$ (OD) $_{6}$ Cl $_{2}$ 0.6D $_{2}$ Oは $_{rm N}$ =7.2K以下で磁気秩序を示し、負のベクトルスピンキラリティーを持つ=0の磁気構造が現れる。0.3Kでの秩序モーメントは0.58(2)Bに抑えられている。我々のDFT計算では、この系が量子臨界点の近くにあり、 $J_{1}$ - $J_{2}$ - $J_{d}$ カゴメ反強磁性体の優れた実現であることを示唆している。

論文

Horizontal line nodes in SrRuO proved by spin resonance

飯田一樹*; 古府麻衣子; 鈴木雄大*; 村井直樹; 河村聖子; 梶本亮一; 稲村泰弘; 石角元志*; 長谷川舜介*; 益田隆嗣*; et al.

Journal of the Physical Society of Japan, 89(5), p.053702_1 - 053702_5, 2020/05

https://doi.org/10.7566/JPSJ.89.053702

被引用回数：23 パーセンタイル：78.59(Physics, Multidisciplinary)

We investigated the low-energy incommensurate (IC) magnetic fluctuations in SrRuO by the high-resolution inelastic neutron scattering measurements and random phase approximation (RPA) calculations. We observed a spin resonance with energy of $hbar omega_{rm res}0.56$ meV centered at a characteristic wavevector $Q_{rm res}=(0.3,0.3,0.5)$ . The resonance energy corresponds well to the superconducting gap 2 = 0.56 meV estimated by the tunneling spectroscopy. The spin resonance shows the modulation with a maximum at around . The modulated intensity of the spin resonance and our RPA calculations indicate that the superconducting gaps regarding the quasi-one-dimensional and sheets at the Fermi surfaces have the horizontal line nodes. These results may set a strong constraint on the pairing symmetry of SrRuO. We also discuss the implications on possible superconducting order parameters.

論文

Lattice dynamics in FeSe via inelastic X-ray scattering and first-principles calculations

村井直樹; 福田竜生; 中島正道*; 河村光晶*; 石川大介*; 田島節子*; Baron, A. Q. R.*

Physical Review B, 101(3), p.035126_1 - 035126_6, 2020/01

https://doi.org/10.1103/PhysRevB.101.035126

被引用回数：7 パーセンタイル：34.47(Materials Science, Multidisciplinary)

非弾性X線散乱を用いたFeSe超伝導体のフォノン研究について報告する。実験的に決定したフォノン分散と非磁性相の密度汎関数理論(DFT)とを比較を行うと、両所の間には顕著な不一致が見られた。FeSeは磁気秩序を示さないにもかかわらず、スピン偏極DFTを用いることによって初めて実験結果は再現される。この解析は、強いスピン揺らぎを内在した常時性状態における近似を与える。

論文

Experimental investigation of the suppressed superconducting gap and double-resonance mode in Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$

出田真一郎*; 村井直樹; 中島正道*; 梶本亮一; 田中清尚*

Physical Review B, 100(23), p.235135_1 - 235135_7, 2019/12

https://doi.org/10.1103/PhysRevB.100.235135

被引用回数：3 パーセンタイル：13.18(Materials Science, Multidisciplinary)

Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$ has an exotic physical property where that the C $_{2}$ -SDW phase suddenly changes to the C $_{4}$ -magnetic phase and superconductivity is suppressed within a narrow composition range around x = 0.25. We have investigated the doping dependence of the electronic structure of Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$ using angle-resolved photoemission spectroscopy (ARPES) and found an anomaly in the superconducting (SC) gap structure only for x = 0.25 in both the hole and electron Fermi surfaces (FSs). We also propose that the mechanism of a newly observed double-resonance peak by inelastic neutron scattering is understandable by the SC gap obtained by ARPES. Our discovery reveals the important relationship between the C $_{4}$ - magnetic phase and superconductivity, and provides an opportunity to survey the underlying relationship between the SC gap and resonance mode in the hole-doped iron-based superconductor.

論文

非弾性X線散乱で見る鉄系超伝導体の格子ダイナミクスと磁性の関係

村井直樹; 福田竜生; 田島節子*; Baron, A. Q. R.*

放射光, 32(4), p.199 - 208, 2019/07

鉄系超伝導体は2008年に国内で発見された新しいタイプの高温超伝導体である。我々は、SPring-8の高分解能非弾性X線散乱を用いたフォノン分散測定から、同物質で実現されるスピン・フォノン結合の存在を明らかにした。特に、構造・磁気秩序相で形成されるマルチドメイン構造を抑制するために、一軸圧力下でのフォノン測定を行い、4回回転対称性を破る磁気秩序によって誘発されるフォノン分散構造の異方性の観測に初めて成功した。第一原理フォノン計算を組み合わせた解析を用いることで、鉄系超伝導体のフォノン構造におけるスピン揺らぎの重要性が示された。

論文

Coexisting spin resonance and long-range magnetic order of Eu in EuRbFe $_{4}$ As $_{4}$

飯田一樹*; 永井佑紀; 石田茂之*; 石角元志*; 村井直樹; Christianson, A. D.*; 吉田紘行*; 稲村泰弘; 中村博樹; 中尾朗子*; et al.

Physical Review B, 100(1), p.014506_1 - 014506_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.014506

被引用回数：39 パーセンタイル：83.48(Materials Science, Multidisciplinary)

パルス中性子散乱実験による鉄系超伝導体EuRbFe $_{4}$ As $_{4}$ のスピン揺らぎ、磁気構造の測定を行い、同物質における超伝導体対称性などの議論を行った。

論文

Study on use of superconducting magnet and first inelastic neutron scattering experiment under magnetic field at 4SEASONS spectrometer

梶本亮一; 石角元志*; 吉良弘*; 金子耕士; 中村充孝; 蒲沢和也*; 稲村泰弘; 池内和彦*; 飯田一樹*; 村井直樹; et al.

Physica B; Condensed Matter, 556, p.26 - 30, 2019/03

BB2018-0570.pdf:2.17MB

https://doi.org/10.1016/j.physb.2018.11.065

被引用回数：3 パーセンタイル：13.18(Physics, Condensed Matter)

Magnets are important for studying magnetism and are commonly used as sample environment devices of neutron scattering instruments. However, the use of magnets was prevented at the time-of-flight direct-geometry neutron spectrometer 4SEASONS in Materials and Life Science Experimental Facility (MLF) at J-PARC, because the instrument is surrounded by iron components, and it is equipped with a piece of equipment operated with magnetic bearings. In the present work, we investigate the influence of stray magnetic fields from a superconducting magnet which is shared among neutron scattering instruments in MLF. Based on the investigation, we modified 4SEASONS such that it can be used with the magnet. Finally, we successfully performed the first inelastic neutron scattering experiments with applied magnetic fields using this sample environment.

論文

Quantum magnetisms in uniform triangular lattices Li $_{2}$ Mo $_{3}$ O $_{8}$ ( = In, Sc)

飯田一樹*; 吉田紘行*; 岡部博孝*; 片山尚幸*; 石井裕人*; 幸田章宏*; 稲村泰弘; 村井直樹; 石角元志*; 門野良典*; et al.

Scientific Reports (Internet), 9(1), p.1826_1 - 1826_9, 2019/02

https://doi.org/10.1038/s41598-018-36123-7

被引用回数：14 パーセンタイル：65.80(Multidisciplinary Sciences)

Molecular based spin-1/2 triangular lattice systems have attracted research interest. LiMoO ( = In or Sc) is such a compound where spin-1/2 MoO $_{13}$ clusters in place of Mo ions form the uniform triangular lattice. Here, we report exotic magnetisms in LiInMoO and LiScMoO investigated by muon spin rotation (SR) and inelastic neutron scattering (INS) spectroscopies. LiInMoO exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the 120 $^{circ}$ spin structure. In contrast, LiScMoO undergoes short-range magnetic order below 4 K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.