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石飛 尊之
Journal of the Physical Society of Japan, 94(7), p.075001_1 - 075001_2, 2025/07
We show that superzone gap formation-phenomena usually attributed to antiferroic ordering-can also arise from ferroic orders in materials featuring sublattice structures. Through an analysis of a 
-orbital tight-binding model on a zigzag chain, we reveal that ferroquadrupolar or ferromagnetic ordering, as well as external magnetic fields, can generate a Su-Schrieffer-Heeger-type gap.
久保 勝規
Journal of the Physical Society of Japan, 94(7), p.074701_1 - 074701_5, 2025/07
Surface states of a tight-binding model with nearest-neighbor hopping on a diamond lattice of finite thickness are investigated. We consider systems with (001), (110), and (111) surfaces. Even if the surface direction is fixed, there is freedom to choose the surface structure due to the two-sublattice nature of a diamond lattice. The existence of surface states is governed by the topology of the matrix elements of the bulk Hamiltonian. In this sense, the existence of surface states is determined by the bulk Hamiltonian. However, the matrix elements depend on the choice of the unit cell, which should be chosen to conform to the surface structure. Thus, the surface states depend on the surface structure. We find that for each surface direction, there are two choices of surface structure, and depending on the chosen structure, the corresponding surface states emerge in distinct regions of the surface Brillouin zone.
門野 良典*; 伊藤 孝
Journal of the Physical Society of Japan, 94(6), p.064601_1 - 064601_11, 2025/06
We extend the previously published model that distinguishes between the diffusive motion of diamagnetic muons and the dynamics of ions around the muon in matter, and propose a generalized model for 
(Mu
s, bound states of a muon and an unpaired electron) observed in non-metallic host materials. The new model distinguishes among the independent motion of unpaired electron associated with Mu, the self-diffusive motion of Mu as single atomic entity, and that of the ions surrounding Mu, where the muon spin relaxation is induced by dynamical fluctuations of the hyperfine (HF) field exerted from the unpaired electron (e.g., due to spin/charge exchange reaction) and/or that of the nuclear hyperfine (NHF) interactions between the unpaired electron and the surrounding ions. We have applied this model to the muonated radicals (Mus in a polaron state) in conducting polymers, and examined the validity of the interpretations claimed in the earlier literature that the spin relaxation is induced by quasi-one dimensional jump motion of the unpaired electron. The result suggests that experimental support for such a claim is still inadequate and needs to be reexamined, including the possibility of other origins for the fluctuations. It is expected that our model will prove a useful guide for 
SR studies of various local dynamics involving paramagnetic muon states.
町田 晃彦*; 齋藤 寛之*; 青木 勝敏*; 小松 一生*; 服部 高典; 佐野 亜沙美; 舟越 賢一*; 町田 真一*; 佐藤 豊人*; 折茂 慎一*
Physical Review B, 111(22), p.224413_1 - 224413_6, 2025/06
Mn金属を高温高圧で水素化することにより形成される反強磁性Mn重水素化物、fcc
-MnDxとhcp
-MnDxの結晶構造と磁気構造をin-situ中性子粉末回折により調べた。重水素原子はfcc及びhcp金属格子の八面体格子間を部分的に占有していた。N
el温度は-MnD
で543(10)Kであった。-MnD
では、飽和磁気モーメントは0.82(1)
、Nel温度は347(3)Kであった。-MnDと-MnDについて決定されたNel温度は、以前の研究で提案されたそれぞれのSlater-Pauling曲線によって予測されたものと一致した。更新されたNel温度は、電子バンド構造計算に基づくより正確なSlater-Pauling曲線の開発に示唆を与える。
Co
)Sn studied by SRCai, Y.*; Yoon, S.*; Sheng, Q.*; Zhao, G.*; Seewald, E. F.*; Ghosh, S.*; Ingham, J.*; Pasupathy, A. N.*; Queiroz, R.*; Lei, H.*; et al.
Physical Review B, 111(21), p.214412_1 - 214412_17, 2025/06
We study the magnetic properties of the metallic kagome system (FeCo)Sn by a combination of muon spin relaxation (SR), magnetic susceptibility, and scanning tunneling microscopy (STM) measurements in single crystal specimens with Co concentrations 
= 0, 0.11, 0.8. In the undoped antiferromagnetic compound FeSn, we find possible signatures for a previously unidentified phase that sets in at 
~K, well beneath the Neel temperature 
~K as indicated by a peak in the relaxation rate 1/
observed in zero field (ZF) and longitudinal field (LF) SR measurements, with a corresponding anomaly in the ac and dc susceptibility, and an increase in the static width 1/
in ZF-SR measurements. No signatures of spatial symmetry breaking are found in STM down to 7~K. Related to the location and motion of muons in FeSn, we confirmed a previous report that about 40% of the implanted muons reside at a field-cancelling high symmetry site at 
~K, while an onset of thermal hopping changes the site occupancy at higher temperatures. In Fe
Co
Sn, where disorder eliminated the field-cancellation effect, all the implanted muons exhibit precession and/or relaxation in the ordered state. In Fe
Co
Sn, we find canonical spin glass behavior with freezing temperature 
~K; the ZF and LF-SR time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of 
at 
and 
as 
. The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by SR in many geometrically frustrated spin systems on insulating kagome, pyrochlore, and triangular lattices. The spin glass behavior of CoSn doped with dilute Fe moments is shown to originate primarily from the randomness of doped Fe moments rather than due to geometrical frustration of the underlying lattice.
松下 太樹*; 小沢 耀弘*; 荒木 康史; 藤本 純治*; 佐藤 昌利*
Physical Review B, 111(24), p.245131_1 - 245131_11, 2025/06
We investigate the intrinsic spin Nernst effect (SNE), a transverse spin current induced by temperature gradients, in topological Dirac semimetals (TDSMs) and magnetic Weyl semimetals (MWSMs) with Ising spin-orbit coupling. The intrinsic SNE is described by the spin Berry curvature, which reflects the geometric nature of TDSMs and MWSMs. We clarified that the intrinsic SNE becomes significant when the Fermi energy is near, but slightly deviates from, the energy of the point nodes. In this situation, Bloch electrons with strong spin Berry curvature contribute to the SNE while avoiding carrier compensation between electrons and holes. We found that in TDSMs with small Fermi surfaces, the spin Nernst angle, which measures the efficiency of the SNE, is larger than that observed in heavy metals. This suggests that TDSMs with small Fermi surfaces can achieve efficient heat-to-spin current conversion. In MWSMs, variation in the magnitude of the exchange coupling with magnetic moments significantly changes the SNE, affecting both the direction and magnitude of the spin Nernst current. This implies that ferromagnetic transitions can be used to reverse the spin Nernst current. These results provide the fundamentals for future topological spin caloritronics.
Sud, A.*; 山本 慧; 飯浜 賢志*; 石橋 一晃*; 深見 俊輔*; 紅林 秀和*; 水上 成美*
Physical Review Letters, 134(24), p.246704_1 - 246704_7, 2025/06
We investigate the nonlinear coupling between acoustic (ac) and optical (op) modes in the coupled magnetization dynamics of synthetic antiferromagnets (SyAFs), utilizing current-driven resonance spectroscopy. A clear spectral splitting is evident in the ac mode when strongly excited by the radio frequency (RF) current at the driving frequency half that of the op mode resonance. The Landau-Lifshitz phenomenology aligns with the experimental observations, affirming the coupling of the RF-excited ac and op modes through three-magnon mixing. The nonlinearity enables a Rabi-like splitting in in-plane magnetized SyAF without breaking its natural symmetries. This discovery holds potential for advancing our understanding of nonlinear antiferromagnetic dynamics.
Go, G.*; Goli, D. P.*; 江崎 蘭世; Tserkovnyak, Y.*; Kim, S. K.*
Physical Review Research (Internet), 7(2), p.L022066_1 - L022066_7, 2025/06
It remains an open question whether or not the scalar spin chirality itself can exhibit a Hall-type transport. In this work, we show that the answer is yes: The scalar spin chirality is Hall-transported in Kagome ferromagnets and antiferromagnets under an external bias, engendering a phenomenon which we dub the scalar spin chirality Nernst effect. Our findings call for the need to lift the conventional assumption that the scalar spin chirality is a static quantity in order to discover the active roles of the scalar spin chirality in transport properties.
目黒 智成*; 小沢 耀弘*; 小林 浩二*; 荒木 康史; 野村 健太郎*
Physical Review Research (Internet), 7(2), p.L022065_1 - L022065_8, 2025/06
We theoretically find a topological spin-orbit torque (SOT) in the compensated ferrimagnetic Weyl semimetal Ti
MnAl. The topological SOT arises from all the occupied states, which is free from dissipation. However, it is negligible in metallic magnets and was not reported in Weyl semimetals. We show the enhancement of the topological SOT from the mixed Berry curvature around the Weyl points in TiMnAl. This finding provides a guiding principle for designing highly efficient SOT devices using the topological nature of ferrimagnetic Weyl semimetals.
orbital system on a simple cubic lattice久保 勝規
Journal of the Physical Society of Japan, 94(5), p.054703_1 - 054703_7, 2025/05
A tight-binding model for orbitals on a simple cubic lattice with finite thickness is investigated. The hopping integrals for nearest-neighboring sites are considered. We examine the electronic band structures for systems with (001), (110), and (111) surfaces. Electronic states well localized around the surfaces are found for the (110) and (111) surfaces. In particular, the surface state is flat and extends in the entire Brillouin zone for the (111) surface, provided the bulk band projected onto the surface Brillouin zone is gapped. We also find that these surface states possess octupole moments in both the (110) and (111) surface cases.
phases in undoped and Ca-modified sodium niobates阿蘇 星侑*; 松尾 拓紀*; 米田 安宏; 森川 大輔*; 津田 健治*; 大山 研司*; 石垣 徹*; 野口 祐二*
Physical Review B, 111(17), p.174114_1 - 174114_12, 2025/05
高分解能放射光X線・中性子回折、収束電子線回折、密度汎関数理論(DFT)計算を組合せた解析により、Ca修飾NaNbO
と非ドープNaNbOの結晶構造、phase転移、相安定性を調べた。その結果、Ca修飾によって反強誘電体(AFE)-相が200Kから800Kの広い温度範囲で安定化されること、NaNbO
は格子膨張を伴う温度誘起等方圧によって安定化されるのに対し、Ca修飾NaNbOは格子収縮を伴う組成誘起化学圧力によって安定化されることが示された。
under pressureKnafo, W.*; Thebault, T.*; Raymond, S.*; Manuel, P.*; Khalyavin, D. D.*; Orlandi, F.*; Ressouche, E.*; Beauvois, K.*; Lapertot, G.*; 金子 耕士; et al.
Physical Review X, 15(2), p.021075_1 - 021075_16, 2025/05
The discovery of multiple superconducting phases in UTe boosted research on correlated-electron physics. This heavy-fermion paramagnet was rapidly identified as a reference compound to study the interplay between magnetism and unconventional superconductivity with multiple degrees of freedom. The proximity to a ferromagnetic quantum phase transition was initially proposed as a driving force to triplet-pairing superconductivity. However, we find here that long-range incommensurate antiferromagnetic order is established under pressure. The propagation vector k
= (0.07, 0.33, 1) of the antiferromagnetic phase is close to a wavevector where antiferromagnetic fluctuations have previously been observed at ambient pressure. These elements support that UTe is a nearly-antiferromagnet at ambient pressure. Our work appeals for theories modelling the evolution of the magnetic interactions and electronic properties, driving a correlated paramagnetic regime at ambient pressure to a long-range antiferromagnetic order under pressure. A deeper understanding of itinerant-f-electrons magnetism in UTe will be a key for describing its unconventional superconducting phases.
山内 宏樹; 目時 直人; 綿貫 竜太*; Hong, T.*; Fernandez-Baca, J. A.*; 萩原 雅人; 益田 隆嗣*; 吉沢 英樹*; 伊藤 晋一*
Journal of the Physical Society of Japan, 94(5), p.054705_1 - 054705_8, 2025/04
The 
-electron states of NdB were determined by observing crystalline electric field (CEF) excitations with inelastic neutron scattering experiments. Our analysis yields CEF excitation energies of 2.8, 12.4, 17.2, and 25.4 meV. The -electron states are simply described by one of 
-multiplets 
with negligibly small mixing. The ground state is the pseudo-quartet consist of the ground doublet dominated by 
and the first excited doublet dominated by 
at 2.8 meV, which is consistent with magnetic specific heat and entropy reported in earlier study. The simple -electron states in NdB are the consequence of the strong uniaxial and in-plane isotropic CEF potential due to the local structure of Nd
ions with point symmetry 
.
松谷 悠佑; 吉井 勇治*; 楠本 多聞*; 小川 達彦; 大西 世紀*; 平田 悠歩; 佐藤 達彦; 甲斐 健師
Physical Chemistry Chemical Physics, 27(14), p.6887 - 6898, 2025/04
被引用回数：0 パーセンタイル：0.00(Chemistry, Physical)水の放射線分解により生成されるラジカルは、DNA損傷誘発、染色体異常、発がんなど、放射線による生物影響の評価において重要な役割を果たす。粒子および重イオン輸送コードシステム(PHITS)では、あらゆる荷電粒子について水中の原子相互作用を推定できる飛跡構造解析モードと、ラジカルをシミュレート可能な電子線専用の化学コード(PHITS-Chem)が先行研究にて開発された。本研究では、あらゆるイオンビームに適用可能なPHITS-Chemコードを開発すると同時に、化学種間の反応をより効率的に検出する空間分割法や化学種の4次元可視化機能を整備した。更新されたPHITS-Chemコードは、文献にて報告される陽子線、
粒子線、炭素イオン線のG値と比較することにより検証され、PHITSオリジナル3次元描画ソフトPHIG-3Dによりラジカルの拡散動態を直感的に評価することに成功した。また、空間分割法の導入により、計算精度を維持しながら計算時間を大幅に短縮(約28倍高速化)することにも成功した。開発したPHITS-Chemコードは、粒子線治療においてラジカルにより誘発される生物効果の正確かつ直感的な理解に貢献することが期待される。
玉造 博夢; 内原 猛*; 満田 節生*; 石井 祐太*; 中尾 裕則*; 竹端 寛治*; 今中 康貴*
Physical Review B, 111(13), p.134403_1 - 134403_9, 2025/04
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)In multiferroic CuFe
Al
O, applying uniaxial pressure generates a magnetoferroelectric phase distinct from the well-studied spin-driven ferroelectric phase associated with helical magnetic ordering in this system. Using a four-circle neutron diffractometer, the magnetic structure of the -induced magnetoferroelectric phase is determined as the collinear sinusoidal type, which itself does not break the inversion symmetry in this system. Additionally, synchrotron radiation X-ray diffraction experiments are conducted to investigate how the triangular lattice in CuFeAlO is distorted by applied . Although lattice distortion during the magnetic phase transition in CuFeAlO is mitigated by the substitution of nonmagnetic Al, the application of along the conjugate direction revives the "latent" spin-lattice coupling, causing the triangular lattice to distort during magnetic phase transition. The application of a magnetic filed considerably reduces -induced ferroelectric polarization, but does not affect lattice distortion. These results indicate that -induced ferroelectric polarization is not a consequence of the piezoelectric effect. Instead, the sinusoidal magnetic structure would contribute to the emergence of -induced ferroelectric polarization through spin-lattice coupling.
under hydrostatic pressure; A Combined neutron, X-ray, Raman, and first-principles calculation studyEfthimiopoulos, I.*; Klotz, S.*; Kunc, K.*; Baptiste, B.*; Chauvigne, P.*; 服部 高典
Physical Review B, 111(13), p.134103_1 - 134103_13, 2025/04
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)X線回折、中性子回折、ラマン散乱、第一原理計算を用いて、ReOの高圧力下での挙動を15GPaまで包括的に調べた。常圧
=3
構造は0.7GPaで空間群
=3の立方晶相に連続的に相転移し、その後少なくとも15GPaまで安定であることがわかった。過去この圧力領域で報告されていた単斜晶
構造や菱面体晶=3
構造への転移は、試料に高輝度放射光X線を照射したことによる試料の劣化によるものであり、人工的なものであることが分かった。また今回、=3相の構造の圧力依存性と正確な状態方程式および天然試料と同位体濃縮
O試料のラマン散乱データを示した。このデータから、リジッドなReO
八面体が圧力とともに回転することによって、相転移および高密度化が起こることが分かった。
Md produced in the 
He + 
Es reaction西尾 勝久; 廣瀬 健太郎; 牧井 宏之; Orlandi, R.; Kean, K. R.*; 塚田 和明; 豊嶋 厚史*; 浅井 雅人; 佐藤 哲也; Chiera, N. M.*; et al.
Physical Review C, 111(4), p.044609_1 - 044609_12, 2025/04
被引用回数：0In spontaneous fission (SF) it is found that the mass-asymmetric fission of well-known actinides suddenly changes to the symmetric fission when nucleus has a mass number 
larger than 257. We have measured for the first time fission-fragment mass and total-kinetic-energy (TKE) distributions of the excited compound nucleus Md, populated in the reaction He+Es, using the rare isotope Es with a short half-life, 
=276 days. The fission of Md can be interpreted as involving 3 fission modes: an mass-asymmetric mode and two modes of mass-asymmetric fissions, the latter two are manifested by different TKE values. Predominantly symmetric fission was obtained at the excitation energy of 15.0 MeV. By increasing the energy to 18.0 MeV, the asymmetric fission mode dominates. Both such a strong change of fission modes within a small increase of excitation energy and the enhancement of asymmetric split are new phenomena in fission.
中堂 博之; 横井 直人*; 松尾 衛; 針井 一哉*; 鈴木 淳*; 今井 正樹; 佐藤 正寛*; 前川 禎通*; 齊藤 英治*
Physical Review Letters, 134(13), p.130603_1 - 130603_5, 2025/04
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)A spin 1/2 is the simplest system that has been believed to support a single two-level quantum system, represented by a single resonance. We experimentally demonstrate that a spin-1/2 nucleus of 
F in C
F exhibits an extra resonance corresponding to the emergence of the states, by mechanically rotating a sample and a coil in nuclear magnetic resonance (NMR) measurements. On the basis of the Floquet formalism, we identify the emergence of the extra two-level state due to the temporal periodicity generated by the mechanical rotation (mechanical spin multiplexing) and derive an operator algebra analogous to the planar rotor algebra in an effective description of the system. The observed multiplexing allows a single spin 1/2 to carry more than two states and potentially enabling the processing of multiple quantum bits on a single spin.
Rajeev, H. S.*; Hu, X.*; Chen, W.-L.*; Zhang, D.*; Chen, T.*; 古府 麻衣子*; 梶本 亮一; 中村 充孝; Chen, A. Z.*; Johnson, G. C.*; et al.
Journal of the Physical Society of Japan, 94(3), p.034602_1 - 034602_14, 2025/03
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)Two-dimensional hybrid organic-inorganic perovskites (HOIPs) have emerged as promising materials for light-emitting diode applications. In this study, by using time-of-flight neutron spectroscopy we identified and quantitatively separated the lattice vibrational and molecular rotational dynamics of two perovskites, butylammonium lead iodide (BA)PbI
and phenethyl-ammonium lead iodide (PEA)PbI. By examining the corresponding temperature dependence, we found that the lattice vibrations, as evidenced by neutron spectra, are consistent with the lattice dynamics obtained from Raman scattering. We revealed that the rotational dynamics of organic molecules in these materials tend to suppress their photoluminescence quantum yield (PLQY) while the vibrational dynamics did not show predominant correlations with the same. Additionally, we observed photoluminescence emission peak splitting for both systems, which becomes prominent above certain critical temperatures where the suppression of PLQY begins. This study suggests that the rotational motions of polarized molecules may lead to a reduction in exciton binding energy or the breaking of degeneracy in exciton binding energy levels, enhancing non-radiative recombination rates, and consequently reducing photoluminescence yield. These findings offer a deeper understanding of fundamental interactions in 2D HOIPs and could guide the design of more efficient light-emitting materials for advanced technological applications.
日高 宏之*; 柳谷 駿*; 小野寺 進太朗*; 柳澤 達也*; 網塚 浩*; 谷田 博司*; 石飛 尊之
Journal of the Physical Society of Japan, 94(3), p.034706_1 - 034706_9, 2025/03
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)We investigated the magnetic-field direction anisotropy of the unknown ordered phase in the tetragonal compound CeCoSi through bulk physical property measurements. The anisotropy in the field direction, previously identified in X-ray diffraction experiments, where a field-induced phase appears along [100] but not along [110], was confirmed in the bulk properties. Combining these experimental results with Landau theory, we infer that the field-induced phase in the [100] direction emerges under an infinitesimally small magnetic field.
