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論文

Intrinsic spin Nernst effect in topological Dirac and magnetic Weyl semimetals

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

https://doi.org/10.1103/dlt5-zxm9
 被引用回数：0

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.

論文

Neutron diffraction study of the crystal and magnetic structures of antiferromagnetic manganese deuteride at high temperatures and high pressures

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

https://doi.org/10.1103/yf8k-cy61
 被引用回数：1

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$$gamma$$-MnDxとhcp$$epsilon$$-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$'{e}$el温度は$$gamma$$-MnD$$_{0.34}$$で543(10)Kであった。$$epsilon$$-MnD$$_{0.62}$$では、飽和磁気モーメントは0.82(1)$$mu_B$$、N$'{e}$el温度は347(3)Kであった。$$gamma$$-MnD$$_{0.34}$$と$$epsilon$$-MnD$$_{0.62}$$について決定されたN$'{e}$el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N$'{e}$el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。

論文

Magnetism of kagome metals (Fe$$_{1-x}$$Co$$_x$$)Sn studied by $$mu$$SR

Cai, 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

https://doi.org/10.1103/PhysRevB.111.214412
 被引用回数：0

We study the magnetic properties of the metallic kagome system (Fe$$_{1-x}$$Co$$_x$$)Sn by a combination of muon spin relaxation ($$mu$$SR), magnetic susceptibility, and scanning tunneling microscopy (STM) measurements in single crystal specimens with Co concentrations $$x$$ = 0, 0.11, 0.8. In the undoped antiferromagnetic compound FeSn, we find possible signatures for a previously unidentified phase that sets in at $$T^{*}sim 50$$~K, well beneath the Neel temperature $$T_{N}sim 376$$~K as indicated by a peak in the relaxation rate 1/$$T_1$$ observed in zero field (ZF) and longitudinal field (LF) $$mu$$SR measurements, with a corresponding anomaly in the ac and dc susceptibility, and an increase in the static width 1/$$T_2$$ in ZF-$$mu$$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 $$T < 250$$~K, while an onset of thermal hopping changes the site occupancy at higher temperatures. In Fe$$_{0.89}$$Co$$_{0.11}$$Sn, where disorder eliminated the field-cancellation effect, all the implanted muons exhibit precession and/or relaxation in the ordered state. In Fe$$_{0.2}$$Co$$_{0.8}$$Sn, we find canonical spin glass behavior with freezing temperature $$T_gsim 3.5$$~K; the ZF and LF-$$mu$$SR time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of $$1/T_1$$ at $$T_g$$ and $$1/T_1to 0$$ as $$Tto 0$$. The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by $$mu$$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.

論文

Electrically controlled nonlinear magnon-magnon coupling in a synthetic antiferromagnet

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

https://doi.org/10.1103/sc6y-rxbg
 被引用回数：1

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.

論文

Scalar spin chirality Nernst effect

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

https://doi.org/10.1103/y3m6-25rw

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.

論文

Topological spin-orbit torque in ferrimagnetic Weyl semimetal

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

https://doi.org/10.1103/PhysRevResearch.7.L022065

We theoretically find a topological spin-orbit torque (SOT) in the compensated ferrimagnetic Weyl semimetal Ti$$_{2}$$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 Ti$$_{2}$$MnAl. This finding provides a guiding principle for designing highly efficient SOT devices using the topological nature of ferrimagnetic Weyl semimetals.

論文

Crystal structures and phase stability of antiferroelectric $$R$$ 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

https://doi.org/10.1103/PhysRevB.111.174114

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$$_{3}$$と非ドープNaNbO$$_{3}$$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)-$$R$$相が200Kから800Kの広い温度範囲で安定化されること、NaNbO$$_3$$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$$_3$$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。

論文

Incommensurate antiferromagnetism in UTe$$_2$$ under pressure

Knafo, 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

https://doi.org/10.1103/PhysRevX.15.021075
 被引用回数：0

The discovery of multiple superconducting phases in UTe$$_2$$ 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$$_{rm m}$$ = (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$$_2$$ 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$$_2$$ will be a key for describing its unconventional superconducting phases.

論文

Crystal structures of ReO$$_3$$ under hydrostatic pressure; A Combined neutron, X-ray, Raman, and first-principles calculation study

Efthimiopoulos, 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

https://doi.org/10.1103/PhysRevB.111.134103
 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$$_3$$の高圧力下での挙動を15GPaまで包括的に調べた。常圧$$Pm$$=3$$m$$構造は0.7GPaで空間群$$Im$$=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$$C2/c$$構造や菱面体晶$$R$$=3$$c$$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、$$Im$$=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$$^{18}$$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$$_6$$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。

論文

Magnetoferroelectric phase transition induced by latent spin-lattice coupling in the geometrically frustrated magnet $$mathrm{CuFe_{0.95}Al_{0.05}O_{2}}$$

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

https://doi.org/10.1103/PhysRevB.111.134403
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

In multiferroic CuFe$$_{0.95}$$Al$$_{0.05}$$O$$_{2}$$, applying uniaxial pressure $$p$$ 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 $$p$$-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 CuFe$$_{0.95}$$Al$$_{0.05}$$O$$_{2}$$ is distorted by applied $$p$$. Although lattice distortion during the magnetic phase transition in CuFe$$_{0.95}$$Al$$_{0.05}$$O$$_{2}$$ is mitigated by the substitution of nonmagnetic Al$$^{3+}$$, the application of $$p$$ 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 $$p$$-induced ferroelectric polarization, but does not affect lattice distortion. These results indicate that $$p$$-induced ferroelectric polarization is not a consequence of the piezoelectric effect. Instead, the sinusoidal magnetic structure would contribute to the emergence of $$p$$-induced ferroelectric polarization through spin-lattice coupling.

論文

Competition between mass-symmetric and asymmetric fission modes in $$^{258}$$Md produced in the $$^{4}$$He + $$^{254}$$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

https://doi.org/10.1103/PhysRevC.111.044609
 被引用回数：0 パーセンタイル：0.00(Physics, Nuclear)

In 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 $$A_{c}$$ larger than 257. We have measured for the first time fission-fragment mass and total-kinetic-energy (TKE) distributions of the excited compound nucleus $$^{258}$$Md, populated in the reaction $$^{4}$$He+$$^{254}$$Es, using the rare isotope $$^{254}$$Es with a short half-life, $$T_{1/2}$$=276 days. The fission of $$^{258}$$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.

論文

Mechanical multiplexer of nuclear spin states

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

https://doi.org/10.1103/PhysRevLett.134.130603
 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 $$^{19}$$F in C$$_{6}$$F$$_{6}$$ 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.

論文

Spontaneous magnetic field and disorder effects in BaPtAs$$_{1-x}$$Sb$$_x$$ with a honeycomb network

足立 匡*; Ogawa, Taiki*; 小宮山 陽太*; 須村 拓也*; Saito-Tsuboi, Yuki*; Takeuchi, Takaaki*; Mano, Kohei*; Manabe, Kaoru*; 川端 幸樹*; 今津 毅士*; et al.

Physical Review B, 111(10), p.L100508_1 - L100508_6, 2025/03

https://doi.org/10.1103/PhysRevB.111.L100508
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

Chiral superconductivity exhibits the formation of novel electron pairs that breaks the time-reversal symmetry and has been actively studied in various quantum materials in recent years. However, despite its potential to provide definitive information, effects of disorder in the crystal structure on the chiral superconductivity has not yet been clarified, and therefore the investigation using a solid-solution system is desirable. We report muon-spin-relaxation ($$mu$$SR) results of layered pnictide BaPtAs$$_{1-x}$$Sb$$_x$$ with a honeycomb network composed of Pt and (As, Sb). We observed an increase of the zero-field $$mu$$SR rate in the superconducting (SC) state at the Sb end of $$x=1.0$$, suggesting the occurrence of a spontaneous magnetic field due to the time-reversal symmetry breaking in the SC state. On the other hand, a spontaneous magnetic field was almost and completely suppressed for the As-Sb mixed samples of $$x=0.9$$ and 0.2, respectively, suggesting that the time-reversal symmetry-breaking SC state in $$x=1.0$$ is sensitive to disorder. The magnetic penetration depth estimated from transverse-field $$mu$$SR measurements at $$x=1.0$$ and 0.2 behaved like weak-coupling $$s$$-wave superconductivity. These seemingly incompatible zero-field and transverse-field $$mu$$SR results of BaPtAs$$_{1-x}$$Sb$$_x$$ with $$x=1.0$$ could be understood in terms of chiral $$d$$-wave superconductivity with point nodes on the three-dimensional Fermi surface.

論文

Nonreciprocal resonant surface acoustic wave absorption in Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

Ba, Y.*; 山本 慧; 他6名*

Physical Review B, 111(10), p.104401_1 - 104401_15, 2025/03

https://doi.org/10.1103/PhysRevB.111.104401
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

Ferrimagnet insulator yttrium iron garnet (Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$, YIG) attracts much interest in magnonics and microwave applications due to its relatively low magnetic damping and long magnon relaxation time. The magnetoelastic interaction between YIG magnetization and surface acoustic waves (SAWs) has been the basis in the development of acoustic-surface-wave isolators. However, the investigation of SAW-driven magnetic resonance in YIG is limited by the low compatibility of YIG and SAW devices. In this work, we demonstrate nonreciprocal resonant SAW absorption in an on-chip YIG-SAW device integrated by the focused ion beam technique. We observed two distinct SAW absorption signals attributed to the perpendicular standing spin waves (PSSW). Furthermore, the large observed nonreciprocity is compared to theoretical predictions incorporating the influence of asymmetric surface conditions on PSSW mode profiles and nonreciprocal magnon-SAW coupling. The strongly nonreciprocal SAW attenuation in YIG offers a promising opportunity for highly efficient rf signal processing technologies.

論文

Intrinsic low-temperature magnetic properties on ultraclean UTe$$_2$$ with $$T_c$$ = 2.1 K revealed by $$^{125}$$Te NMR

松村 拓輝*; 徳永 陽; 酒井 宏典; 神戸 振作; 他13名*

Physical Review B, 111(9), p.094507_1 - 094507_9, 2025/03

https://doi.org/10.1103/PhysRevB.111.094507
 被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)

To investigate the intrinsic magnetic properties of UTe$$_2$$, we performed $$^{125}$$Te-NMR measurements on the ultra-clean single-crystalline UTe$$_2$$ with superconducting transition temperature $$T_c$$ = 2.1 K and compared the results with those of the $$T_c$$ = 1.6 K sample. The broadening of the linewidth of the NMR spectrum in the a-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6 K sample are suppressed in the ultra-clean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe$$_2$$ are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the a-axis as the magnetic easy axis.

論文

Spin-singlet ground state with spin gap in $$S_{rm eff}$$ = $$frac{1}{2}$$ antiferromagnetic tetramer compound Yb$$_2$$SiO$$_5$$

長谷 正司*; 金子 耕士; 田端 千紘; 山内 宏樹; 辻井 直人*; D$"o$nni, A.*

Physical Review B, 111(9), p.094403_1 - 094403_9, 2025/03

https://doi.org/10.1103/PhysRevB.111.094403
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

We studied magnetic properties of Yb$$_2$$SiO$$_5$$ having pseudospins of $$S_{rm eff}$$ = $$frac{1}{2}$$ using magnetization, specific heat, and inelastic neutron scattering (INS) measurements. We observed cluster-like excitations in the INS measurements. We determined that the spin system in Yb$$_2$$SiO$$_5$$ is the $$S_{rm eff}$$ = $$frac{1}{2}$$ AFM tetramer with two exchange interactions of $$J_1 = 0.74$$ and $$J_2 = 0.95$$~meV. The spin tetramer can explain the excitation energies, $$chi (T)$$, magnetic specific heat at $$T < 15$$~K, and the magnitude of the scattering vector ($$Q$$) dependence of the intensity [$$I(Q)$$] at 0.7 and 1.2 meV. The spin tetramer, however, cannot explain well $$I(Q)$$ at 1.9 meV and $$I(T)$$ of the three excitations probably due to effects of weak inter-tetramer interactions.

論文

Magnetic and quadrupole coupling emerging in NdB$$_4$$ with geometrically frustrated orthogonal antiferromagnetic dimer

目時 直人; 山内 宏樹; 萩原 雅人; 綿貫 竜太*; 河村 聖子; 古府 麻衣子*; 中島 健次; 松田 雅昌*

Physical Review B, 111(10), p.104424_1 - 104424_9, 2025/03

https://doi.org/10.1103/PhysRevB.111.104424
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

フラストレートしたシャストリ・サザランド格子を有するNdB$$_4$$の磁気転移を理解する目的で中性子非弾性散乱実験を行った。$$|pm frac{5}{2}rangle$$と$$|pm frac{7}{2}rangle$$による準四重項状態が磁気秩序相で4つに分裂する。スペクトルは磁気相互作用$$langle J_x rangle J_x$$、磁気$$J_x$$と四極子$$O_{zx}$$の結合、そして一軸的な結晶場により説明される。この$$f$$電子状態により、主たる秩序変数である面内磁気モーメント$$m_perp=langle J_x rangle$$と結く誘起された2次的な秩序変数$$m_c=langle J_z rangle$$を説明することができた。幾何学的フラストレーションによってハイゼンベルグ相互作用が打ち消し合う状況で、磁気と四極子の結合が本質的な役割をすることが明らかになった。

論文

Comprehensive Bayesian machine learning approach to estimating the total nuclear capture rate of a negative muon

岩元 大樹; 新倉 潤*; 水野 るり恵*

Physical Review C, 111(3), p.034614_1 - 034614_13, 2025/03

https://doi.org/10.1103/PhysRevC.111.034614
 被引用回数：0 パーセンタイル：0.00(Physics, Nuclear)

1$$s$$軌道上の負ミューオンは原子核に捕獲され、原子核崩壊過程を引き起こす。負ミューオンの全核捕獲率は、地球化学、宇宙核物理学、半導体デバイス開発などの分野できわめて重要であるが、現在の物理理論モデルによる正確な予測は依然として困難である。本研究では、ベイズ統計の枠組みで物理理論の情報と実験データを統合し、負ミューオンの全核捕獲率を推定する包括的な機械学習(ML)モデルを開発することを目的とした。本研究では、ガウス過程回帰に基づくMLモデルを採用し、不確かさが評価された実験データを学習データとして用いた。このモデルは事前情報としてGoulard-Primakoffの式を取り入れ、特にデータが乏しい領域での推定を可能にするために、転移学習の方法を適用した。開発したMLモデルは、精度と包括性の両方において物理理論モデルを上回ることが示され、モデル性能をさらに向上させるための重要な実験が特定された。本研究で生成された推定値は、ミューオン核データに組み込まれ、様々な研究分野に応用される予定である。

論文

Transverse asymmetry of individual $$gamma$$ rays in the $$^{139}$$La($$overrightarrow{n},gamma$$)$$^{140}$$La reaction

奥泉 舞桜*; Auton, C. J.*; 遠藤 駿典; 藤岡 宏之*; 広田 克也*; 猪野 隆*; 石崎 貢平*; 木村 敦; 北口 雅暁*; 古賀 淳*; et al.

Physical Review C, 111(3), p.034611_1 - 034611_6, 2025/03

https://doi.org/10.1103/PhysRevC.111.034611
 被引用回数：0 パーセンタイル：0.00(Physics, Nuclear)

The observed enhancement of Parity Violation in the vicinity of p-wave compound nuclear resonances for a variety of medium-heavy nuclei can be understood using the sp-mixing model. The sp-mixing model predicts several neutron energy-dependent angular correlations between the spin and momentum of neutron and $$gamma$$-ray emitted from (n,$$gamma$$) reactions. In this work, the correlation term $$overrightarrow{sigma_textrm{n}}cdot(overrightarrow{k_textrm{n}}timesoverrightarrow{k_gamma})$$ in the $$^{139}$$La($$overrightarrow{n}$$,$$gamma$$)$$^{140}$$La$$^ast$$ reaction was measured precisely and a significant transverse asymmetry was found in the transition to the excited states of $$^{140}$$La.

論文

Production and in-medium modification of $$phi$$ mesons in proton-nucleus reactions from a transport approach

Gubler, P.; 市川 真也; Song, T.*; Bratkovskaya, E.*

Physical Review C, 111(3), p.034908_1 - 034908_12, 2025/03

https://doi.org/10.1103/PhysRevC.111.034908
 被引用回数：1 パーセンタイル：90.19(Physics, Nuclear)

Production and in-medium modification of hidden strange $$phi$$ mesons are studied in proton-nucleus reactions: p+C, p+Cu, and p+Pb at 12 GeV/c, partially measured by the KEK E325 Collaboration via the dilepton decay mode. This work is based on the off-shell microscopic parton-hadron-string dynamics transport approach, and especially makes it possible to simulate in-medium off-shell dynamics of the $$phi$$ meson in the reactions studied. Different in-medium scenarios for the modification of the $$phi$$ meson spectral function in nuclear matter are investigated: (i) dropping pole mass, (ii) collisional broadening, and (iii) simultaneous dropping pole mass and collisional broadening. Even though the $$phi$$ meson production in p+A reactions occurs only at densities around or below normal nuclear matter density $$rho_0$$, we find visible modifications of the generated dilepton spectra for the in-medium scenarios compared to the vacuum distribution.

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