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Liu, P.-F.*; Li, X.*; Li, J.*; Zhu, J.*; Tong, Z.*; 古府 麻衣子*; 楡井 真実; Xu, J.*; Yin, W.*; Wang, F.*; et al.
National Science Review, 11(12), p.nwae216_1 - nwae216_10, 2024/12
被引用回数：13 パーセンタイル：94.32(Multidisciplinary Sciences)Crystalline solids exhibiting inherently low lattice thermal conductivity (
) are of great importance in applications such as thermoelectrics and thermal barrier coatings. However, cannot be arbitrarily low and is limited by the minimum thermal conductivity related to phonon dispersions. In this work, we report the liquid-like thermal transport in a well-ordered crystalline CsAg
Te
, which exhibits an extremely low value of 
0.18 Wm
K. On the basis of first-principles calculations and inelastic neutron scattering measurements, we find that there are lots of low-lying optical phonon modes at 3.1 meV hosting the avoided-crossing behavior with acoustic phonons. These strongly localized modes are accompanied by weakly bound rattling Ag atoms with thermally induced large amplitudes of vibrations. Using the two-channel model, we demonstrate that coupling of the particle-like phonon modes and the heat-carrying wave-like phonons is essential for understanding the low , which is heavily deviated from the 
temperature dependence of the standard Peierls theory. In addition, our analysis indicates that the soft structural framework with liquid-like motions of the fluctuating Ag atoms is the underlying cause that leads to the suppression of the heat conduction in CsAgTe. These factors synergistically account for the ultralow value. Our results demonstrate that the liquid-like heat transfer could indeed exist in a well-ordered crystal.
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
被引用回数：2 パーセンタイル：0.00(Materials Science, Multidisciplinary)Our result provides an important foundation for an accurate analysis of the inverse Rashba-Edelstein effect induced by thermal spin injection.
佐野 涼太郎*; 大湊 友也*; 松尾 衛
Physical Review Letters, 132(23), p.236302_1 - 236302_9, 2024/06
被引用回数：4 パーセンタイル：82.50(Physics, Multidisciplinary)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.
船戸 匠*; 松尾 衛; 加藤 岳生*
Physical Review Letters, 132(23), p.236201_1 - 236201_7, 2024/06
被引用回数：6 パーセンタイル：82.50(Physics, Multidisciplinary)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.
Yao, D.*; 松尾 衛; 横山 毅人*
Applied Physics Letters, 124(16), p.162603_1 - 162603_5, 2024/04
被引用回数：4 パーセンタイル：78.60(Physics, Applied)We propose a mechanism of spin current generation under an external electric field due to chiral phonons in a chiral-structure superconductor based on the Bogoliubov de Gennes and the Boltzmann equations.
-MgAgSbLi, J.*; Li, X.*; Zhang, Y.*; Zhu, J.*; Zhao, E.*; 古府 麻衣子; 中島 健次; Avdeev, M.*; Liu, P.-F.*; Sui, J.*; et al.
Applied Physics Reviews (Internet), 11(1), p.011406_1 - 011406_8, 2024/03
被引用回数：11 パーセンタイル：89.71(Physics, Applied)The desire for intrinsically low lattice thermal conductivity (
) in thermoelectrics motivates numerous efforts on understanding the microscopic mechanisms of heat transport in solids. Here, based on theoretical calculations, we demonstrate that -MgAgSb hosts low-energy localized phonon bands and avoided crossing of the rattler modes, which coincides with the inelastic neutron scattering result. Using the two-channel lattice dynamical approach, we find, besides the conventional contribution (70% at 300 K) from particlelike phonons propagating, the coherence contribution dominated by the wavelike tunneling of phonons accounts for 30% of total at 300 K. By considering dual contributions, our calculated room-temperature of 0.64 WmK well agrees with the experimental value of 0.63 WmK. More importantly, our computations give a nonstandard 
dependence, perfectly explaining the abnormal temperature-trend of 
in experiment for -MgAgSb. By molecular dynamics simulation, we reveal that the structure simultaneously has soft crystalline sublattices with the metavalent bonding and fluctuating liquid-like sublattices with thermally induced large amplitude vibrations. These diverse forms of chemical bonding arouse mixed part-crystal part-liquid state, scatter strongly heat-carrying phonons, and finally produce extremely low . The fundamental research from this study will accelerate the design of ultralow- materials for energy-conversion applications.
大湊 友也*; 山影 相*; 松尾 衛
Physical Review B, 109(12), p.L121405_1 - L121405_5, 2024/03
被引用回数：2 パーセンタイル：57.35(Materials Science, Multidisciplinary)We study a dynamical spin response of surface Majorana modes in a topological superconductor-magnet hybrid under microwave irradiation. We find a method to toggle between dissipative and nondissipative Majorana Ising spin dynamics by adjusting the external magnetic field angle and the microwave frequency. This reflects the topological nature of the Majorana modes, enhancing the Gilbert damping of the magnet, thereby providing a detection method for the Majorana Ising spins. Our findings illuminate a magnetic probe for Majorana modes, paving the path to innovative spin devices.
松島 悠*; Zhang, Z.*; 大橋 由梨*; 畠山 紘*; Xiao, G.*; 船戸 匠*; 松尾 衛; 海住 英生*
Applied Physics Letters, 124(2), p.022404_1 - 022404_7, 2024/01
被引用回数：3 パーセンタイル：70.50(Physics, Applied)We report the discovery of a stepwise magnetic field-induced emergent magneto-inductance effect in Permalloy thin films deposited on polycarbonate substrates. This study opens up exciting avenues for advancing our understanding of emergent inductance in fundamental physics and paves the way for practical applications in flexible magnetic devices.
Zhang, A.*; Deng, K.*; Sheng, J.*; Liu, P.*; Kumar, S.*; 島田 賢也*; Jiang, Z.*; Liu, Z.*; Shen, D.*; Li, J.*; et al.
Chinese Physics Letters, 40(12), p.126101_1 - 126101_8, 2023/12
被引用回数：11 パーセンタイル：85.96(Physics, Multidisciplinary)In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, itis predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral "Dirac-like" fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Here, by combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.
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
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
Ni
BiO
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.
SnSeRen, Q.*; Gupta, M. K.*; Jin, M.*; Ding, J.*; Wu, J.*; Chen, Z.*; Lin, S.*; Fabelo, O.*; Rodriguez-Velamazan, J. A.*; 古府 麻衣子; et al.
Nature Materials, 22(8), p.999 - 1006, 2023/08
被引用回数：78 パーセンタイル：99.19(Chemistry, Physical)Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite AgSnSe using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed 'liquid-like thermal conduction' picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (
0.5 WmK) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.
SnS-based shandite filmsLau, Y.-C.*; 池田 絢哉*; 藤原 宏平*; 小沢 耀弘*; Zheng, J.*; 関 剛斎*; 野村 健太郎*; Du, L.*; Wu, Q.*; 塚崎 敦*; et al.
Physical Review B, 108(6), p.064429_1 - 064429_11, 2023/08
被引用回数：11 パーセンタイル：72.60(Materials Science, Multidisciplinary)Magnetic Weyl semimetals (mWSMs) are characterized by linearly dispersive bands with chiral Weyl node pairs associated with broken time-reversal symmetry. One of the hallmarks of mWSMs is the emergence of large intrinsic anomalous Hall effect. On heating the mWSM above its Curie temperature, the magnetism vanishes while exchange-split Weyl point pairs collapse into doubly degenerate gapped Dirac states. Here, we reveal the attractive potential of these Dirac nodes in paramagnetic state for efficient spin current generation at room temperature via the spin Hall effect. Ni and In are introduced to separately substitute Co and Sn in a prototypal mWSM CoSnS shandite film and tune the Fermi level. Composition dependence of spin Hall conductivity for paramagnetic shandite at room temperature resembles that of anomalous Hall conductivity for ferromagnetic shandite at low temperature; exhibiting peak-like dependence centering around the Ni-substituted CoNi
SnS and undoped CoSnS compositions, respectively. The observed spin Hall and anomalous Hall conductivity maxima at different compositions reflect optimum Fermi-level positioning relative to the paramagnetic Dirac and magnetic Weyl states, suggesting the common origin and intercorrelation between the two Hall effects. Our findings highlight a strategy for the quest of spin Hall materials, guided by the abundant experimental anomalous Hall-effect data of ferromagnets in the literature.
佐野 涼太郎*; 松尾 衛
Physical Review Letters, 130(16), p.166201_1 - 166201_7, 2023/04
被引用回数：5 パーセンタイル：59.55(Physics, Multidisciplinary)Recent experiments have shown an indication of a hydrodynamic magnon behavior in ultrapure ferromagnetic insulators; however, its direct observation is still lacking. Here, we derive a set of coupled hydrodynamic equations and study the thermal and spin conductivities for such a magnon fluid. We reveal the drastic breakdown of the magnonic Wiedemann-Franz law as a hallmark of the hydrodynamics regime, which will become key evidence for the experimental realization of an emergent hydrodynamic magnon behavior. Therefore, our results pave the way toward the direct observation of magnon fluids.
BaCo(PO
)Sheng, J.*; Wang, L.*; Candini, A.*; Jiang, W.*; Huang, L.*; Xi, B.*; Zhao, J.*; Ge, H.*; Zhao, N.*; Fu, Y.*; et al.
Proceedings of the National Academy of Sciences of the United States of America, 119(51), p.e2211193119_1 - e2211193119_9, 2022/12
被引用回数：34 パーセンタイル：93.63(Multidisciplinary Sciences)Although considerable progress has been made in the theoretical understanding of the low-dimensional frustrated quantum magnets, experimental realizations of a well-established scaling analysis are still scarce. This is particularly true for the two-dimensional antiferromagnetic triangular lattices. Owing to the small exchange strength, the newly discovered compound NaBaCo(PO) provides a rare opportunity for clarifying the quantum criticality in an ideal triangular lattice with quantum spin S=1/2. In addition to the establishment of the complete phase diagrams, the spin Hamiltonian with a negligible interplane interaction has been determined through the spin wave dispersion in the polarized state, which is consistent with the observation of a two-dimensional quantum critical point with the Bose-Einstein condensation of diluted free bosons.
K
(Zn
Mn
)
As studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering鈴木 博人*; Zhao, G.*; 岡本 淳*; 坂本 祥哉*; Chen, Z.-Y.*; 野中 洋亮*; 芝田 悟朗; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.
Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06
被引用回数：2 パーセンタイル：0.00(Physics, Multidisciplinary)The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor BaK(ZnMn)As have been studied by X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering (RIXS). The sum rule analysis of the XMCD spectra indicates that the Mn atoms are in the high-spin configurations of 
, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. Based on a comparison of the RIXS line shapes with those of GaMnAs, it is concluded that the ground state of Mn in BaK(ZnMn)As consists of both the 
and 
electron configurations.
船戸 匠*; 松尾 衛
Journal of Magnetism and Magnetic Materials, 540, p.168436_1 - 168436_7, 2021/12
被引用回数：4 パーセンタイル：22.00(Materials Science, Multidisciplinary)We theoretically study the mechanical induction of the spin density via the Rashba spin-orbit interaction (SOI). The spin density in the linear response to lattice distortion dynamics is calculated based on the microscopic theory. We reveal that there are two mechanisms of spin induction: one is the acoustic Edelstein effect (AEE) from the acceleration of the lattice dynamics and the other is caused by the Rashba spin-vorticity coupling (RSVC). We find that the AEE induces a more efficient spin-to-charge conversion in comparison with the conventional electric Edelstein effect. The induced spin density due to the RSVC is expressed as a Berry curvature-like quantity; therefore, it can be attributed to the spatial symmetry breaking due to the Rashba SOI. Our work demonstrates high-efficiency spin generation in Rashba systems.
山本 剛史*; 加藤 岳生*; 松尾 衛
Physical Review B, 104(12), p.L121401_1 - L121401_5, 2021/09
被引用回数：7 パーセンタイル：41.33(Materials Science, Multidisciplinary)We investigate the spin Seebeck effect and spin pumping in a junction between a ferromagnetic insulator and a magnetic impurity deposited on a normal metal. By performing a numerical renormalization group calculation, we show that spin current is enhanced by the Kondo effect. This spin current is suppressed by an increase in temperature or a magnetic field comparable to the Kondo temperature. Our results indicate that spin transport can be a direct probe of spin excitation in strongly correlated systems.
山 正樹*; 立野 雅大*; 加藤 岳生*; 松尾 衛
Physical Review B, 104(5), p.054410_1 - 054410_9, 2021/08
被引用回数：10 パーセンタイル：50.62(Materials Science, Multidisciplinary)We theoretically consider spin pumping in a junction between a ferromagnetic insulator (FI) and a two-dimensional electron gas (2DEG) in which the Rashba and Dresselhaus spin-orbit interactions coexist. Using second-order perturbation theory, we derive an increase in linewidth in the case of an interfacial exchange coupling in a ferromagnetic resonance (FMR) experiment. We clarify how the enhancement of Gilbert damping depends on the resonant frequency and spin orientation of the FI. We show that this setup of an FMR experiment can provide information on the spin texture of 2DEG at the Fermi surface.
船戸 匠*; 松尾 衛
Physical Review B, 104(6), p.L060412_1 - L060412_5, 2021/08
被引用回数：3 パーセンタイル：17.11(Materials Science, Multidisciplinary)We theoretically study spin transport in two- or three-dimensional Rashba systems dynamically distorted by surface acoustic waves. The spin currents in the linear response to lattice distortion dynamics are calculated on the basis of a microscopic theory combined with local coordinate transformations. As a result, we find a mechanism of direct spin-current generation from lattice distortion not associated with a charge current or spin accumulation. Moreover, the in-plane helicity currents are generated by shear surface acoustic waves via the present mechanism. The generated helicity currents are not parallel to the vorticity of the lattice, and cannot be created with the conventional methods. Thus, our findings offer an alternative functionality of the conventional Rashba systems in the field of spintronics.
仲田 光樹; 大沼 悠一*; 松尾 衛*
Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04
被引用回数：5 パーセンタイル：22.39(Materials Science, Multidisciplinary)マグノン流に内在する量子力学的性質「量子ゆらぎ物性」をスピン流雑音の観点から理論的に研究し、マグノン流の非可換性由来の非対称マグノン流量子雑音を解明した。
