Updated on 2024/10/18

写真a

 
ADACHI Hiroto
 
Organization
Research Institute for Interdisciplinary Science Associate Professor
Position
Associate Professor
External link

Degree

  • 博士(理学) ( 京都大学 )

Research Areas

  • Nanotechnology/Materials / Applied condensed matter physics  / スピントロニクス

  • Natural Science / Magnetism, superconductivity and strongly correlated systems

Education

  • 京都大学大学院理学研究科   物理学・宇宙物理学専攻 博士後期課程  

    2000.4 - 2003.11

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  • 京都大学大学院理学研究科   物理学・宇宙物理学専攻 修士課程  

    1998.4 - 2000.3

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  • 京都大学理学部    

    1994.4 - 1998.3

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Research History

  • - 岡山大学異分野基礎科学研究所 准教授

    2016.4

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  • - Associate Professor,Research Institute for Interdisciplinary Science,Okayama University

    2016

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  • 日本原子力研究開発機構   研究副主幹

    2014.4 - 2016.3

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  • 日本原子力研究開発機構   任期付き研究員

    2011.4 - 2014.3

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  • 日本原子力研究開発機構   博士研究員

    2010.4 - 2011.3

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  • Tohoku University   Institute for Materials Research

    2009.3 - 2010.3

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  • スイス連邦工科大学チューリッヒ校   日本学術振興会海外特別研究員

    2007.3 - 2009.2

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  • Okayama University   The Graduate School of Natural Science and Technology

    2003.12 - 2007.2

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Papers

  • Time-dependent Ginzburg-Landau theory of the vortex spin Hall effect Reviewed

    Hiroto Adachi, Yusuke Kato, Jun-ichiro Ohe, Masanori Ichioka

    Physical Review B   2024.5

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    DOI: 10.1103/PhysRevB.109.174503

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  • Ginzburg-Landau action and polarization current in an excitonic insulator model of electronic ferroelectricity Reviewed

    Hiroto Adachi, Naoshi Ikeda, Eiji Saitoh

    Physical Review B   2023.4

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    DOI: 10.1103/PhysRevB.107.155142

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  • Fluctuation contribution to spin Hall effect in superconductors Reviewed

    Akimitsu Watanabe, Hiroto Adachi, Yusuke Kato

    Physical Review B   2022.9

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    DOI: 10.1103/PhysRevB.106.104504

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  • Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation Reviewed

    Yutaka Yamamoto, Masanori Ichioka, Hiroto Adachi

    Physical Review B   105 ( 10 )   2022.3

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    Publishing type:Research paper (scientific journal)   Publisher:American Physical Society ({APS})  

    DOI: 10.1103/PhysRevB.105.104417

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  • Spin Hall effect generated by fluctuating vortices in type-II superconductors Reviewed

    Takuya Taira, Yusuke Kato, Masanori Ichioka, Hiroto Adachi

    Physical Review B   103 ( 13 )   2021.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We theoretically investigate the vortex spin Hall effect, i.e., a novel spin Hall effect driven by the motion of superconducting vortices, by focusing on the role of superconducting fluctuations. Within the BCS-Gor'kov microscopic approach combined with the Kubo formula, we find a strong similarity between the vortex spin Hall effect and the vortex Nernst/Ettingshausen effect. Calculated temperature dependence of the voltage signal due to the inverse vortex spin Hall effect exhibits a strong enhancement by vortex fluctuations. This result not only provides a possible explanation for a prominent peak found in the spin Seebeck effect in a NbN/Y3Fe5O12 system but also leads to a proposal of new experiments using other superconductors with strong fluctuations, such as cuprate or iron-based superconductors.

    DOI: 10.1103/PhysRevB.103.134417

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  • Nonmagnetic impurity effect in vortex states of chiral superconductors Reviewed

    Ueda, Takahiro, Sera, Yasuaki, Adachi, Hiroto, Ichioka, Masanori

    Physical Review B   103 ( 1 )   2021

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    Nonmagnetic impurity scattering effects in the vortex states are studied in the Born and the unitary limits for chiral superconductors by Eilenberger theory. We compare the spatial structure of the pair potential and local electronic structure in chiral p-wave superconductors with those in two types of chiral d-wave superconductors; d(1 +/-) d(xz) +/- id(yz) and d(2 +/-) d(x2-y2 )+/- id(xy) pairing Similar behaviors of the pair potentials are seen in p +/- - and d(1 +/-) -wave superconductors. In chiral d-wave superconductors, due to lack of Majorana properties relating to the s-wave Cooper pair amplitude, zero-energy vortex bound states are easily destroyed by the impurity scattering, compared to the Born limit in the chiral p_-wave superconductors. This decay is also seen in the unitary limit in the chiral p_ -wave superconductors. These differences are also discussed in the relation to s-wave Cooper pair amplitude and the local scattering rate. The impurity effects are also compared with those in s-wave superconductors.

    DOI: 10.1103/PHYSREVB.103.014506

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  • Spin pumping into a spin glass material Reviewed

    Yusei Fujimoto, Masanori Ichioka, Hiroto Adachi

    PHYSICAL REVIEW B   101 ( 18 )   2020.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    Spin pumping is a recently established means for generating a pure spin current, whereby spins are pumped from a magnet into the adjacent target material under the ferromagnetic resonance condition. We theoretically investigate the spin pumping from an insulating ferromagnet into spin glass materials. Combining a dynamic theory of spin glasses with the linear-response formulation of the spin pumping, we calculate temperature dependence of the spin pumping near the spin glass transition. The analysis predicts that a characteristic peak appears in the spin pumping signal, reflecting that the spin fluctuations slow down upon the onset of spin freezing.

    DOI: 10.1103/PhysRevB.101.184412

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  • Variation of zero-energy density of states of a d-wave superconductor in a rotating in-plane magnetic field: Effect of nonmagnetic impurities Reviewed

    Yuuki Hashitani, Kenta K. Tanaka, Hiroto Adachi, Masanori Ichioka

    PHYSICAL REVIEW B   101 ( 6 )   2020.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    Oscillation of zero-energy density of states under the rotation of an in-plane magnetic field is used to identify node positions of the superconducting gap. Based on Eilenberger theory that can capture the vortex core contribution appropriately, we quantitatively study the effects of nonmagnetic impurity scattering on the oscillation in a d(x2-y2) -wave superconductor, as a function of the magnetic field and the scattering rate in the Born and the unitary limits. We find that the sign of the oscillation can be changed by the impurity scattering at low fields, indicating that impurity effect is an important factor in the analysis of angle-resolved specific heat measurements.

    DOI: 10.1103/PhysRevB.101.060501

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  • Relation of Superconducting Pairing Symmetry and Non-Magnetic Impurity Effects in Vortex States Reviewed

    Yasuaki Sera, Takahiro Ueda, Hiroto Adachi, Masanori Ichioka

    SYMMETRY-BASEL   12 ( 1 )   2020.1

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:MDPI  

    Non-magnetic impurity scattering effects on the vortex core states are theoretically studied to clarify the contributions from the sign-change of the pairing function in anisotropic superconductors. The vortex states are calculated by the Eilenberger theory in superconductors with px-wave pairing symmetry, as well as the corresponding anisotropic s-wave symmetry. From the spatial structure of the pair potential and the local electronic states around a vortex, we examine the differences between anisotropic superconductors with and without sign-change of the pairing function, and estimate how twofold symmetric vortex core images change with increasing the impurity scattering rate both in the Born and the unitary limits. We found that twofold symmetric vortex core image of zero-energy local density of states changes the orientation of the twofold symmetry with increasing the scattering rate when the sign change occurs in the pairing function. Without the sign change, the vortex core shape reduces to circular one with approaching dirty cases. These results of the impurity effects are valuable for identifying the pairing symmetry by observation of the vortex core image by the STM observation.

    DOI: 10.3390/sym12010175

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  • Spin Seebeck effect in paramagnets and antiferromagnets at elevated temperatures Reviewed

    Yutaka Yamamoto, Masanori Ichioka, Hiroto Adachi

    PHYSICAL REVIEW B   100 ( 6 )   2019.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We develop a theory of the spin Seebeck effect (SSE) in paramagnets as well as in antiferromagnets at elevated temperatures where the classical limit of the fluctuation-dissipation theorem is applicable. Employing dissipative stochastic models that are valid at these temperatures, we calculate the SSE signal, and we find that both the paramagnetic SSE and the antiferromagnetic SSE are expressed by a single equation that is proportional to the external magnetic field times the spin susceptibility of the magnet. The present result suggests the appearance of a cusp structure at the Neel temperature in the antiferromagnetic SSE signal.

    DOI: 10.1103/PhysRevB.100.064419

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  • Spin diffusion equation in superconductors in the vicinity of T-c Reviewed

    Takuya Taira, Masanori Ichioka, So Takei, Hiroto Adachi

    PHYSICAL REVIEW B   98 ( 21 )   2018.12

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    We microscopically derive the spin diffusion equation in an s-wave superconductor in the vicinity of the superconducting transition temperature T-c. Applying the general relation between the relaxation function and the response function to the present spin diffusion problem, we examine how the spin relaxation time and the spin diffusion coefficient are renormalized in the superconducting state. The analysis reveals that, below T-c, both the spin relaxation time and the spin diffusion coefficient are increased, resulting in an enhancement of the spin diffusion length. The present result may provide an explanation for the recent observation of an enhanced spin pumping signal below T-c in a Py/Nb/Pt system that is free from the coherence peak effect.

    DOI: 10.1103/PhysRevB.98.214437

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  • Spin Seebeck effect in a simple ferromagnet near T c: A Ginzburg-Landau approach Reviewed

    Hiroto Adachi, Yutaka Yamamoto, Masanori Ichioka

    Journal of Physics D: Applied Physics   51 ( 14 )   144001(1) - 144001(1)-144001(5)   2018.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Institute of Physics Publishing  

    A time-dependent Ginzburg-Landau theory is used to examine the longitudinal spin Seebeck effect in a simple ferromagnet in the vicinity of the Curie temperature T c. It is shown analytically that the spin Seebeck effect is proportional to the magnetization near T c, whose result is in line with the previous numerical finding. It is argued that the present result can be tested experimentally using a simple magnetic system such as EuO/Pt or EuS/Pt.

    DOI: 10.1088/1361-6463/aab1d1

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  • Spin pumping into superconductors: A new probe of spin dynamics in a superconducting thin film Reviewed

    Masashi Inoue, Masanori Ichioka, Hiroto Adachi

    PHYSICAL REVIEW B   96 ( 2 )   024414(1)-024414(9)   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    Spin pumping refers to the microwave-driven spin current injection from a ferromagnet into the adjacent target material. We theoretically investigate the spin pumping into superconductors by fully taking account of impurity spin-orbit scattering that is indispensable to describe diffusive spin transport with finite spin diffusion length. We calculate temperature dependence of the spin pumping signal and show that a pronounced coherence peak appears immediately below the superconducting transition temperature T-c, which survives even in the presence of the spin-orbit scattering. The phenomenon provides us with a new way of studying the dynamic spin susceptibility in a superconducting thin film. This is contrasted with the nuclear magnetic resonance technique used to study a bulk superconductor.

    DOI: 10.1103/PhysRevB.96.024414

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  • Thermoelectric Generation Based on Spin Seebeck Effects Reviewed

    Ken Ichi Uchida, Hiroto Adachi, Takashi Kikkawa, Akihiro Kirihara, Masahiko Ishida, Shinichi Yorozu, Sadamichi Maekawa, Eiji Saitoh

    Proceedings of the IEEE   104 ( 10 )   1946 - 1973   2016.10

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    © 1963-2012 IEEE. The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in magnetic materials including insulators. The SSE is applicable to thermoelectric generation because the thermally generated spin current can be converted into a charge current via spin-orbit interaction in conductive materials adjacent to the magnets. The insulator-based SSE device exhibits unconventional characteristics potentially useful for thermoelectric applications, such as simple structure, device-design flexibility, and convenient scaling capability. In this article, we review recent studies on the SSE from the viewpoint of thermoelectric applications. Firstly, we introduce the thermoelectric generation process and measurement configuration of the SSE, followed by showing fundamental characteristics of the SSE device. Secondly, a theory of the thermoelectric conversion efficiency of the SSE device is presented, which clarifies the difference between the SSE and conventional thermoelectric effects and the efficiency limit of the SSE device. Finally, we show preliminary demonstrations of the SSE in various device structures for future thermoelectric applications and discuss prospects of the SSE-based thermoelectric technologies.

    DOI: 10.1109/JPROC.2016.2535167

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  • Erratum: Thermoelectric Generation Based on Spin Seebeck Effects (Proceedings of the IEEE (2016) DOI: 10.1109/JPROC.2016.2535167) Reviewed

    Ken Ichi Uchida, Hiroto Adachi, Takashi Kikkawa, Akihiro Kirihara, Masahiko Ishida, Shinichi Yorozu, Sadamichi Maekawa, Eiji Saitoh

    Proceedings of the IEEE   104 ( 7 )   1499   2016.7

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    DOI: 10.1109/JPROC.2016.2577478

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  • Origin of the spin Seebeck effect in compensated ferrimagnets Reviewed

    Stephan Gepraegs, Andreas Kehlberger, Francesco Della Coletta, Zhiyong Qiu, Er-Jia Guo, Tomek Schulz, Christian Mix, Sibylle Meyer, Akashdeep Kamra, Matthias Althammer, Hans Huebl, Gerhard Jakob, Yuichi Ohnuma, Hiroto Adachi, Joseph Barker, Sadamichi Maekawa, Gerrit E. W. Bauer, Eiji Saitoh, Rudolf Gross, Sebastian T. B. Goennenwein, Mathias Klaeui

    NATURE COMMUNICATIONS   7   10452(1)-10452(6)   2016.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:NATURE PUBLISHING GROUP  

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE.

    DOI: 10.1038/ncomms10452

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  • Unconventional scaling and significant enhancement of the spin Seebeck effect in multilayers Reviewed

    R. Ramos, T. Kikkawa, M. H. Aguirre, I. Lucas, A. Anadón, T. Oyake, K. Uchida, H. Adachi, J. Shiomi, P. A. Algarabel, L. Morellón, S. Maekawa, E. Saitoh, M. R. Ibarra

    Physical Review B - Condensed Matter and Materials Physics   92 ( 22 )   220407(1)-220407(5)   2015.12

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    © 2015 American Physical Society. Spin Seebeck effects (SSEs) have been investigated in highly crystalline magnetic multilayer [Fe3O4/Pt]n films. Voltage as well as power generated by the SSE were found to be significantly enhanced with increasing the number of layers n. This voltage enhancement defies the simple understanding of the SSE and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in multilayer SSE systems and the observed voltage enhancement.

    DOI: 10.1103/PhysRevB.92.220407

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  • Magnon instability driven by heat current in magnetic bilayers Reviewed

    Yuichi Ohnuma, Hiroto Adachi, Eiji Saitoh, Sadamichi Maekawa

    PHYSICAL REVIEW B   92 ( 22 )   224404(1)-224404(8)   2015.12

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    We theoretically demonstrate that, in a ferromagnet/paramagnet bilayer, a magnon instability accompanied by a gigahertz microwave emission can be driven simply by means of a temperature bias. Employing many-body theory for investigating the effects of a phonon heat current on the magnon lifetime, we show that the magnon instability occurs upon the suppression of the umklapp scattering at low temperatures, leading to microwave emission. The present finding provides crucial information about the interplay of spin current and heat current.

    DOI: 10.1103/PhysRevB.92.224404

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  • Thermal effects in spintronics: Physics and applications Invited Reviewed

    Hiroto Adachi, Hiroto Adachi, Sadamichi Maekawa, Sadamichi Maekawa

    Handbook of Spintronics   1553 - 1576   2015.9

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    © Springer Science+Business Media Dordrecht 2016. All rights reserved. Recent progress in investigation of the interplay of spin and heat is reviewed. A special emphasis is placed on the newly discovered example of the thermospin phenomenon termed "spin Seebeck effect" which enables the thermal injection of spin currents from a ferromagnet into attached nonmagnetic metals over a macroscopic scale of several millimeters. The theoretical basis for understanding the spin Seebeck effect is presented, and other thermal spin effects are briefly discussed as well.

    DOI: 10.1007/978-94-007-6892-5_54

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  • Back to basics Invited

    Hiroto Adachi

    NATURE PHYSICS   11 ( 9 )   707 - 708   2015.9

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    DOI: 10.1038/nphys3428

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  • Theory of unidirectional spin heat conveyer Reviewed

    Hiroto Adachi, Sadamichi Maekawa

    JOURNAL OF APPLIED PHYSICS   117 ( 17 )   2015.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER INST PHYSICS  

    We theoretically investigate the unidirectional spin heat conveyer effect recently reported in the literature that emerges from the Damon-Eshbach spin wave on the surface of a magnetic material. We develop a simple phenomenological theory for heat transfer dynamics in a coupled system of phonons and the Damon-Eshbach spin wave, and demonstrate that there arises a direction-selective heat flow as a result of the competition between an isotropic heat diffusion by phonons and a unidirectional heat drift by the spin wave. The phenomenological approach can account for the asymmetric local temperature distribution observed in the experiment. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4908019

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  • Generation of spin currents by surface plasmon resonance Reviewed

    K. Uchida, H. Adachi, D. Kikuchi, S. Ito, Z. Qiu, S. Maekawa, E. Saitoh

    Nature Communications   6   2015.1

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    © 2015 Macmillan Publishers Limited. All rights reserved. Surface plasmons, free-electron collective oscillations in metallic nanostructures, provide abundant routes to manipulate light-electron interactions that can localize light energy and alter electromagnetic field distributions at subwavelength scales. The research field of plasmonics thus integrates nano-photonics with electronics. In contrast, electronics is also entering a new era of spintronics, where spin currents play a central role in driving devices. However, plasmonics and spin-current physics have so far been developed independently. Here we report the generation of spin currents by surface plasmon resonance. Using Au nanoparticles embedded in Pt/BiY2Fe5O12 bilayer films, we show that, when the Au nanoparticles fulfill the surface-plasmon-resonance conditions, spin currents are generated across the Pt/BiY2Fe5O12 interface. This spin-current generation cannot be explained by conventional heating effects, requiring us to introduce nonequilibrium magnons excited by surface-plasmon-induced evanescent electromagnetic fields in BiY2Fe5O12. This plasmonic spin pumping integrates surface plasmons with spin-current physics, opening the door to plasmonic spintronics.

    DOI: 10.1038/ncomms6910

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    Other Link: http://orcid.org/0000-0002-6844-6477

  • Theory of the acoustic spin pumping Reviewed

    Hiroto Adachi, Sadamichi Maekawa

    SOLID STATE COMMUNICATIONS   198   22 - 25   2014.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    Spin pumping refers to the spin current injection driven by magnetization dynamics from a ferromagnet into adjacent nonmagnetic conductors. Conventionally, ferromagnetic resonance is used to drive the magnetization dynamics and the spin pumping. Recently a new type of spin pumping driven by acoustic waves, i.e., the acoustic spin pumping, has been reported. We present a linear-response theory of the acoustic spin pumping. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ssc.2014.02.030

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  • Enhanced dc spin pumping into a fluctuating ferromagnet near TC Reviewed

    Yuichi Ohnuma, Hiroto Adachi, Eiji Saitoh, Sadamichi Maekawa

    Physical Review B - Condensed Matter and Materials Physics   89 ( 17 )   2014.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society  

    A linear-response formulation of the dc spin pumping, i.e., a spin injection from a precessing ferromagnet into an adjacent spin sink, is developed in view of describing many-body effects caused by spin fluctuations in the spin sink. It is shown that when an itinerant ferromagnet near TC is used as the spin sink, the spin pumping is largely increased owing to the fluctuation enhancement of the spin conductance across the precessing ferromagnet/spin sink interface. As an example, the enhanced spin pumping from yttrium iron garnet into nickel palladium alloy (TC≃20 K) is analyzed by means of a self-consistent renormalization scheme, and it is predicted that the enhancement can be as large as tenfold. © 2014 American Physical Society.

    DOI: 10.1103/PhysRevB.89.174417

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  • Enhanced dc spin pumping into a fluctuating ferromagnet near T-C Reviewed

    Yuichi Ohnuma, Hiroto Adachi, Eiji Saitoh, Sadamichi Maekawa

    PHYSICAL REVIEW B   89 ( 17 )   174417(1)-174417(10)   2014.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    A linear-response formulation of the dc spin pumping, i.e., a spin injection from a precessing ferromagnet into an adjacent spin sink, is developed in view of describingmany-body effects caused by spin fluctuations in the spin sink. It is shown that when an itinerant ferromagnet near T-C is used as the spin sink, the spin pumping is largely increased owing to the fluctuation enhancement of the spin conductance across the precessing ferromagnet/spin sink interface. As an example, the enhanced spin pumping from yttrium iron garnet into nickel palladium alloy (T-C similar or equal to 20 K) is analyzed by means of a self-consistent renormalization scheme, and it is predicted that the enhancement can be as large as tenfold.

    DOI: 10.1103/PhysRevB.89.174417

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  • Thermal engineering of non-local resistance in lateral spin valves Reviewed

    S. Kasai, S. Hirayama, Y. K. Takahashi, S. Mitani, K. Hono, H. Adachi, J. Ieda, S. Maekawa

    APPLIED PHYSICS LETTERS   104 ( 16 )   162410(1)-162410(4)   2014.4

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    We study the non-local spin transport in Permalloy/Cu lateral spin valves (LSVs) fabricated on thermally oxidized Si and MgO substrates. While these LSVs show the same magnitude of spin signals, significant substrate dependence of the baseline resistance was observed. The baseline resistance shows much weaker dependence on the inter-electrode distance than that of the spin transport observed in the Cu wires. A simple analysis of voltage-current characteristics in the baseline resistance indicates the observed result can be explained by a combination of the Peltier and Seebeck effects at the injector and detector junctions, suggesting the usage of high thermal conductivity substrate (or under-layer) is effective to reduce the baseline resistance. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4873687

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  • Separation of longitudinal spin Seebeck effect from anomalous Nernst effect: Determination of origin of transverse thermoelectric voltage in metal/insulator junctions Reviewed

    T. Kikkawa, K. Uchida, S. Daimon, Y. Shiomi, H. Adachi, Z. Qiu, D. Hou, X. F. Jin, S. Maekawa, E. Saitoh

    Physical Review B - Condensed Matter and Materials Physics   88 ( 21 )   214403(1)-214403(11)   2013.12

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    The longitudinal spin Seebeck effect (LSSE) and the anomalous Nernst effect (ANE) are investigated in various metal/insulator junction systems and a clear separation of the LSSE from the ANE induced by static magnetic proximity is demonstrated. This separation is realized by comparing transverse thermoelectric voltage in in-plane magnetized (IM) and perpendicularly magnetized (PM) configurations, where the LSSE appears only in the IM configuration while the ANE appears both in the IM and PM configurations. We show that, in Pt/Y 3Fe5O12 samples, the LSSE voltage in the IM configuration is three orders of magnitude greater than the proximity-ANE contamination estimated from the data in the PM configuration. This quantitative voltage comparison between the IM and PM configurations is corroborated by systematic voltage measurements in Ni81Fe19/Gd 3Ga5O12, Pt/Gd3Ga5O 12, Au/Y3Fe5O12, and Au/Gd 3Ga5O12 samples and by our phenomenological model calculation. The LSSE measurements in high magnetic field regions further confirm that the observed voltage in the Pt/Y3Fe5O 12 and Au/Y3Fe5O12 samples is of magnon origin. We apply this voltage comparison method also to a Ni 81Fe19/Y3Fe5O12 sample and show that both the LSSE and ANE exist in this sample. © 2013 American Physical Society.

    DOI: 10.1103/PhysRevB.88.214403

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  • Spin current: Experimental and theoretical aspects Reviewed

    Sadamichi Maekawa, Hiroto Adachi, Ken Ichi Uchida, Jun'Ichi Ieda, Eiji Saitoh

    Journal of the Physical Society of Japan   82 ( 10 )   102002(1)-102002(23)   2013.10

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    The flow of electron spin, the so-called "spin current", is a key concept in the recent progress in spintronics. When the spin current interacts with the magnetic moment in a ferromagnetic metal, the angular momentum and energy conservations give rise to the spin transfer torque and spinmotive force, respectively. When it is injected into a nonmagnetic metal attached to a ferromagnet, the electric current is induced through the spin-charge conversion mechanism (inverse spin Hall effect). The generation and manipulation of the spin current and a variety of novel phenomena given by the spin current, including the spin Seebeck effect and spinmotive force, are discussed. © 2013 The Physical Society of Japan.

    DOI: 10.7566/JPSJ.82.102002

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  • Linear-response theory of the longitudinal spin Seebeck effect Reviewed

    Hiroto Adachi, Sadamichi Maekawa

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   62 ( 12 )   1753 - 1758   2013.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:KOREAN PHYSICAL SOC  

    We theoretically investigate the longitudinal spin Seebeck effect, in which the spin current is injected from a ferromagnet into an attached nonmagnetic metal in a direction parallel to the temperature gradient. Using the fact that the phonon heat current flows intensely into the attached nonmagnetic metal in this particular configuration, we show that the sign of the spin injection signal in the longitudinal spin Seebeck effect can be opposite to that in the conventional transverse spin Seebeck effect when the electron-phonon interaction in the nonmagnetic metal is sufficiently large. Our linear-response approach can explain the sign reversal of the spin injection signal recently observed in the longitudinal spin Seebeck effect.

    DOI: 10.3938/jkps.62.1753

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  • Heat and spin Reviewed

    Sadamichi Maekawa, Hiroto Adachi

    Journal of the Korean Physical Society   62 ( 12 )   1985 - 1989   2013.7

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    The thermopower, the so-called Seebeck effect, is the conversion of heat to electricity and is due to the entropy carried by conduction electrons. In strongly-correlated electron systems and Kondo materials, spin fluctuation is shown to bring about an entropy in conduction electrons and to result in a giant thermopower. Recently, the spin Seebeck effect, which reflects the conversion via the spin current in magnetic materials, was discovered. The mechanism is examined and a variety of experiments are explained. © 2013 The Korean Physical Society.

    DOI: 10.3938/jkps.62.1985

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  • Unidirectional spin-wave heat conveyer Reviewed

    T. An, V. I. Vasyuchka, K. Uchida, A. V. Chumak, K. Yamaguchi, K. Harii, J. Ohe, M. B. Jungfleisch, Y. Kajiwara, H. Adachi, B. Hillebrands, S. Maekawa, E. Saitoh

    Nature Materials   12 ( 6 )   549 - 553   2013.6

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    When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe 5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes wit hout time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller. © 2013 Macmillan Publishers Limited. All rights reserved.

    DOI: 10.1038/nmat3628

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  • Theory of the spin Seebeck effect Reviewed

    Hiroto Adachi, Ken Ichi Uchida, Eiji Saitoh, Sadamichi Maekawa

    Reports on Progress in Physics   76 ( 3 )   20   2013.3

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    The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. Recent theoretical and experimental efforts have shown that the magnon and phonon degrees of freedom play crucial roles in the spin Seebeck effect. In this paper, we present the theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal spin effects. © 2013 IOP Publishing Ltd.

    DOI: 10.1088/0034-4885/76/3/036501

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  • Observation of the spin Seebeck effect in epitaxial Fe<inf>3</inf>O <inf>4</inf> thin films Reviewed

    R. Ramos, T. Kikkawa, K. Uchida, H. Adachi, I. Lucas, M. H. Aguirre, P. Algarabel, L. Morellón, S. Maekawa, E. Saitoh, M. R. Ibarra

    Applied Physics Letters   102 ( 7 )   072413(1)-072413(5)   2013.2

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    We report the experimental observation of the spin Seebeck effect in magnetite thin films. The signal observed at temperatures above the Verwey transition is a contribution from both the anomalous Nernst (ANE) and spin Seebeck (SSE) effects. The contribution from the ANE of the Fe3O 4 layer to the SSE is found to be negligible due to the resistivity difference between Fe3O4 and Pt layers. Below the Verwey transition, the SSE is free from the ANE of the ferromagnetic layer and it is also found to dominate over the ANE due to magnetic proximity effect on the Pt layer. © 2013 American Institute of Physics.

    DOI: 10.1063/1.4793486

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  • Spin Seebeck effect in antiferromagnets and compensated ferrimagnets Reviewed

    Yuichi Ohnuma, Hiroto Adachi, Eiji Saitoh, Sadamichi Maekawa

    PHYSICAL REVIEW B   87 ( 1 )   7   2013.1

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    We theoretically investigate the spin Seebeck effect (SSE) in antiferromagnets and ferrimagnets, and show that the SSE vanishes in antiferromagnets but survives in ferrimagnets even at the magnetization compensation point despite the absence of its saturation magnetization. The nonvanishing SSE in ferrimagnets stems from two nondegenerate magnons. We demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across the magnetization compensation point.

    DOI: 10.1103/PhysRevB.87.014423

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  • Spin waves, spin currents and spin seebeck effect Reviewed

    Hiroto Adachi, Sadamichi Maekawa

    Topics in Applied Physics   125   119 - 128   2013

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    The spin Seebeck effect is now established as a universal aspect of ferromagnets that enables thermal injection of spin currents from a ferromagnet into attached nonmagnetic metals over macroscopic scale of several millimeters. We show that the spin-wave degrees of freedom play a crucial role in the spin Seebeck effect. © Springer-Verlag Berlin Heidelberg 2013.

    DOI: 10.1007/978-3-642-30247-3_9

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  • Spin-wave spin current in magnetic insulators Reviewed

    Ken ichi Uchida, Hiroto Adachi, Yousuke Kajiwara, Sadamichi Maekawa, Eiji Saitoh

    Solid State Physics - Advances in Research and Applications   64   1 - 27   2013

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    A spin wave is a collective motion of a magnetic moment in magnetically ordered materials. Although spin waves have been known and investigated for many years, recent research has revealed that the spin wave plays an important role in spintronics as a carrier of spin current, that is, a flow of spin angular momentum. Such a spin-wave spin current is available in magnetic insulators even in the absence of conduction electrons, and thus opens a new route for investigating spintronic phenomenon in magnetic insulators. In this article, we review recent progress in insulator spintronics. © 2013 Elsevier Inc.

    DOI: 10.1016/B978-0-12-408130-7.00001-0

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  • Thermal spin pumping and magnon-phonon-mediated spin-Seebeck effect Reviewed

    K. Uchida, T. Ota, H. Adachi, J. Xiao, T. Nonaka, Y. Kajiwara, G. E.W. Bauer, S. Maekawa, E. Saitoh

    Journal of Applied Physics   111 ( 10 )   103903(1)-103903(12)   2012.5

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    The spin-Seebeck effect (SSE) in ferromagnetic metals and insulators has been investigated systematically by means of the inverse spin-Hall effect (ISHE) in paramagnetic metals. The SSE generates a spin voltage as a result of a temperature gradient in a ferromagnet, which injects a spin current into an attached paramagnetic metal. In the paramagnet, this spin current is converted into an electric field due to the ISHE, enabling the electric detection of the SSE. The observation of the SSE is performed in longitudinal and transverse configurations consisting of a ferromagnet/paramagnet hybrid structure, where thermally generated spin currents flowing parallel and perpendicular to the temperature gradient are detected, respectively. Our results explain the SSE in terms of a two-step process: (1) the temperature gradient creates a non-equilibrium state in the ferromagnet governed by both magnon and phonon propagations and (2) the non-equilibrium between magnons in the ferromagnet and electrons in the paramagnet at the contact interface leads to thermal spin pumping and the ISHE signal. The non-equilibrium state of metallic magnets (e.g., Ni 81Fe 19) under a temperature gradient is governed mainly by the phonons in the sample and the substrate, while in insulating magnets (e.g., Y 3Fe 5O 12), both magnon and phonon propagations appear to be important. The phonon-mediated non-equilibrium that drives the thermal spin pumping is confirmed also by temperature-dependent measurements, giving rise to a giant enhancement of the SSE signals at low temperatures. © 2012 American Institute of Physics.

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  • Acoustic spin pumping: Direct generation of spin currents from sound waves in Pt/Y <inf>3</inf>Fe <inf>5</inf>O <inf>12</inf> hybrid structures Reviewed

    K. Uchida, H. Adachi, T. An, H. Nakayama, M. Toda, B. Hillebrands, S. Maekawa, E. Saitoh

    Journal of Applied Physics   111 ( 5 )   053903(1)-053903(8)   2012.3

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    Using a Pt/Y 3Fe 5O 12 (YIG) hybrid structure attached to a piezoelectric actuator, we demonstrate the generation of spin currents from sound waves. This acoustic spin pumping (ASP) is caused by the sound wave generated by the piezoelectric actuator, which then modulates the distribution function of magnons in the YIG layer and results in a pure-spin-current injection into the Pt layer across the Pt/YIG interface. In the Pt layer, this injected spin current is converted into an electric voltage due to the inverse spin-Hall effect (ISHE). The ISHE induced by the ASP is detected by measuring a voltage in the Pt layer at the piezoelectric resonance frequency of the actuator coupled with the Pt/YIG system. The frequency-dependent measurements enable us to separate the ASP-induced signals from extrinsic heating effects. Our model calculation based on the linear response theory provides us with a qualitative and quantitative understanding of the ASP in the Pt/YIG system. © 2012 American Institute of Physics.

    DOI: 10.1063/1.3688332

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  • Long-range spin Seebeck effect and acoustic spin pumping Reviewed

    K. Uchida, H. Adachi, T. An, T. Ota, M. Toda, B. Hillebrands, S. Maekawa, E. Saitoh

    Nature Materials   10 ( 10 )   737 - 741   2011.10

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    Imagine that a metallic wire is attached to a part of a large insulator, which itself exhibits no magnetization. It seems impossible for electrons in the wire to register where the wire is positioned on the insulator. Here we found that, using a Ni81Fe19/Pt bilayer wire on an insulating sapphire plate, electrons in the wire recognize their position on the sapphire. Under a temperature gradient in the sapphire, surprisingly, the voltage generated in the Pt layer is shown to reflect the wire position, although the wire is isolated both electrically and magnetically. This non-local voltage is due to the coupling of spins and phonons: the only possible carrier of information in this system. We demonstrate this coupling by directly injecting sound waves, which realizes the acoustic spin pumping. Our finding provides a persuasive answer to the long-range nature of the spin Seebeck effect 1-8, and it opens the door to 'acoustic spintronics' in which sound waves are exploited for constructing spin-based devices. © 2011 Macmillan Publishers Limited. All rights reserved.

    DOI: 10.1038/nmat3099

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  • Linear-response theory of spin Seebeck effect in ferromagnetic insulators Reviewed

    Hiroto Adachi, Jun-ichiro Ohe, Saburo Takahashi, Sadamichi Maekawa

    PHYSICAL REVIEW B   83 ( 9 )   094410(1)-094410(6)   2011.3

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    We formulate a linear response theory of the spin Seebeck effect, i.e., a spin voltage generation from heat current flowing in a ferromagnet. Our approach focuses on the collective magnetic excitation of spins, i.e., magnons. We show that the linear-response formulation provides us with a qualitative as well as quantitative understanding of the spin Seebeck effect observed in a prototypical magnet, yttrium iron garnet.

    DOI: 10.1103/PhysRevB.83.094410

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  • Numerical study on the spin Seebeck effect Reviewed

    Jun-ichiro Ohe, Hiroto Adachi, Saburo Takahashi, Sadamichi Maekawa

    PHYSICAL REVIEW B   83 ( 11 )   115118(1)-115118(5)   2011.3

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    Thermally driven spin-wave spin current in a ferromagnetic material (FM) and the resulting electric signal in a normal metal (NM) probe placed on the FM are theoretically investigated by taking into account the fluctuation-dissipation theorem for thermally fluctuating spin at the interface of an FM-NM junction. We develop a numerical technique for calculating the spin Seebeck signal detected by the NM probe, which converts spin current to charge current by the inverse spin Hall effect. The spin current is induced in the NM probe via an exchange interaction when the FM senses the temperature gradient. Numerical simulation clarifies the role of the sample boundary in the spatial distribution of spin current in both FM and NM.

    DOI: 10.1103/PhysRevB.83.115118

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  • Gigantic enhancement of spin Seebeck effect by phonon drag Reviewed

    Hiroto Adachi, Ken Ichi Uchida, Eiji Saitoh, Jun Ichiro Ohe, Saburo Takahashi, Sadamichi Maekawa

    Applied Physics Letters   97 ( 25 )   252506(1)-252506(3)   2010.12

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    We investigate both theoretically and experimentally a gigantic enhancement of the spin Seebeck effect in a prototypical magnet LaY2 Fe 5 O12 at low temperatures. Our theoretical analysis sheds light on the important role of phonons; the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag the low-lying spin excitations. We further argue that this scenario gives a clue to understand the observation of the spin Seebeck effect that is unaccompanied by a global spin current, and predict that the substrate condition affects the observed signal. © 2010 American Institute of Physics.

    DOI: 10.1063/1.3529944

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  • Novel mixed-state thermal transport properties in ultra-clean URu2Si2 Reviewed

    Hiroto Adachi, Manfred Sigrist

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   470   S579 - S580   2010.12

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    The heavy-fermion superconductor URu2Si2 shows an intriguing increase of the thermal conductivity in the mixed-state immediately below the upper critical field H-c2 which is in a sharp contrast to common experience. A brief description of the origin of this behavior is given by focusing on the role of the semi-metallic Fermi surface reconstruction induced by the hidden order phase transition. (C) 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2009.10.024

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  • Spin Seebeck insulator Reviewed

    K. Uchida, J. Xiao, H. Adachi, J. Ohe, S. Takahashi, J. Ieda, T. Ota, Y. Kajiwara, H. Umezawa, H. Kawai, G. E.W. Bauer, S. Maekawa, E. Saitoh

    Nature Materials   9 ( 11 )   894 - 897   2010.11

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    Thermoelectric generation is an essential function in future energy-saving technologies. However, it has so far been an exclusive feature of electric conductors, a situation which limits its application; conduction electrons are often problematic in the thermal design of devices. Here we report electric voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, the magnetic insulator LaY 2Fe5O12 can convert a heat flow into a spin voltage. Attached Pt films can then transform this spin voltage into an electric voltage as a result of the inverse spin Hall effect. The experimental results require us to introduce a thermally activated interface spin exchange between LaY2Fe5O12 and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect. © 2010 Macmillan Publishers Limited. All rights reserved.

    DOI: 10.1038/nmat2856

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  • Observation of longitudinal spin-Seebeck effect in magnetic insulators Reviewed

    Ken Ichi Uchida, Hiroto Adachi, Takeru Ota, Hiroyasu Nakayama, Sadamichi Maekawa, Eiji Saitoh

    Applied Physics Letters   97 ( 17 )   172505(1)-172505(3)   2010.10

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    We propose a longitudinal spin-Seebeck effect (SSE), in which a magnon-induced spin current is injected parallel to a temperature gradient from a ferromagnet into an attached paramagnetic metal. The longitudinal SSE is measured in a simple and versatile system composed of a ferrimagnetic insulator Y3 Fe5 O12 slab and a Pt film by means of the inverse spin-Hall effect. The experimental results highlight the intriguing character of the longitudinal SSE due to its own geometric configuration. © 2010 American Institute of Physics.

    DOI: 10.1063/1.3507386

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  • Probing the dx2-y2-wave Pomeranchuk instability by ultrasound Reviewed

    Hiroto Adachi, Manfred Sigrist

    PHYSICAL REVIEW B   80 ( 15 )   155123(1)-155123(13)(   2009.10

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    Selection rules of ultrasound attenuation and sound-velocity renormalization are analyzed in view of their potential application to identify Pomeranchuk instabilities (electronic nematic phase). It is shown that the transverse sound attenuation along [110] direction is enhanced by the Fermi-surface fluctuations near a d(x2-y2)-wave Pomeranchuk instability, while the attenuation along (100) direction remains unaffected. Moreover the fluctuation regime above the instability is analyzed by means of a self-consistent renormalization scheme. The results could be applied directly to Sr3Ru2O7 which is a potential candidate for a Pomeranchuk instability at its metamagnetic transition in strong magnetic fields.

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  • Anomalous thermal conductivity of semi-metallic superconductors with electron-hole compensation Reviewed

    Hiroto Adachi, Manfred Sigrist

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   77 ( 5 )   053704(1)-053704(4)   2008.5

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    The effects of low carrier density and carrier compensation on mixed-state thermal transport are investigated beyond the quasiclassical approximation. It is shown that, contrary to the usual observations, the interplay of the two effects leads to an increase in the thermal conductivity immediately below the upper critical field H-c2. Our result can account for the anomalous behavior of the mixed-state thermal conductivity near H-c2 recently observed in URu2Si2.

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  • Electronic thermal conductivity in a superconducting vortex state Reviewed

    H. Adachi, P. Miranovic, M. Ichioka, K. Machida

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   463   36 - 39   2007.10

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    The longitudinal component of the electronic thermal conductivity kappa(xx) in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using kappa(xx)(B) as a probe of the pair potential symmetry. (C) 2007 Elsevier B.V. All rights reserved.

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  • Vortex state in a Fulde-Ferrell-Larkin-Ovchinnikov superconductor based on quasiclassical theory Reviewed

    Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

    Physical Review B - Condensed Matter and Materials Physics   76 ( 1 )   014503(1)-014503(10)   2007.7

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    We investigate the vortex state with Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulations suggested for a high-field phase of CeCo In5. On the basis of quasiclassical Eilenberger theory, we calculate the three-dimensional structure of pair potentials, internal magnetic fields, paramagnetic moments, and electronic states for s -wave and d -wave pairings comparatively. The π -phase shift of the pair potential at the FFLO nodal plane or at the vortex core induces sharp peak states in the local density of states and enhances the local paramagnetic moment. We also discuss the NMR spectrum and neutron scattering as methods to detect the FFLO structure. © 2007 The American Physical Society.

    DOI: 10.1103/PhysRevB.76.014503

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  • Quasi-classical calculation of the mixed-state thermal conductivity in s- and d-wave superconductors Reviewed

    Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76 ( 6 )   064708(1)-064708(7)   2007.6

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    To see how superconducting gap structures affect the longitudinal component of mixed-state thermal conductivity K-xx(B), the magnetic-field dependences of K-xx(B) in s- and d-wave superconductors are investigated. Calculations are performed on the basis of the quasi-classical theory of superconductivity by fully taking account of the spatial variation of the normal Green's function, neglected in previous works, by the Brandt-Pesch-Tewordt approximation. On the basis of our result, we discuss the possibility of K-xx(B) measurement as a method of probing the gap structure.

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  • Vortex state in FFLO superconductors Reviewed

    Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 )   593 - 595   2007.3

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    Based on the quasiclassical theory, we investigate the vortex structure in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state suggested for the high. field phase of CeCoIn5. We show that the paramagnetic moments are enhanced at the vortex line and at the nodal plane of the FFLO modulation, and discuss the double peak structure of the NMR spectrum in the FFLO state. (c) 2006 Elsevier B.V. All rights reserved.

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  • Quasiclassical calculation of the quasiparticle thermal conductivity in a mixed state Reviewed

    Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 )   640 - 642   2007.3

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    We report the result of calculation of the quasiparticle thermal conductivity kappa(xx)(del T perpendicular to B) in the vortex state of a two-dimensional superconductor. We compute k(xx) for both s-wave and d-wave superconductors, taking account of the spatial dependence of normal Green's function g, which is neglected in the previous studies using the Brandt-Pesch-Tewordt (BPT) method. Our results indicate that k(xx) based on the BPT method is slightly underestimated due to its incoherent spatial averaging procedure. (c) 2006 Elsevier B.V. All rights reserved.

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  • Thermal conductivity in the vortex state of s-wave and d-wave superconductors Reviewed

    P. Mranovic, H. Adachi, M. Ichioka, K. Machida

    SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION   899   630 - 630   2007

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    Thermal conductivity in the vortex state has been calculated by solving self-consistently Eilenberger quasi-classical equations of superconductivity. Field dependence of thermal conductivity tensor has been calculated for various impurity parameters. We showed the difference in the field dependence between s-wave and d-wave superconductors.

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  • Electronic structure of vortex state in a FFLO superconductor Reviewed

    Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   445   186 - 189   2006.10

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    Vortex states in a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor are microscopically investigated by the quasi-classical Eilenberger theory. We calculate the spatial structure of the pair potential, paramagnetic magnetization (i.e., Knight shift in a magnetic field) and electronic states, including paramagnetic depairing effect in addition to the orbital depairing effect. Topologies of 2 pi phase winding at the vortex line and pi phase shift at the FFLO nodal plane affect the distribution of paramagnetic magnetization and low energy electronic states. We also discuss the NMR resonance line shape observed in the high field phase of CeCoIn5. (c) 2006 Elsevier B.V. All rights reserved.

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  • Basal-plane magnetic anisotropies of high-k d-wave superconductors in a mixed state: A quasiclassical approach Reviewed

    Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75 ( 8 )   084716(1)-084716(9)   2006.8

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    We study the basal-plane anisotropies of reversible magnetization and torque in a mixed state of layered d-wave superconductors based on the quasiclassical version of the BCS-Gor'kov theory. Both the longitudinal magnetization (M-L) and torque (tau) show fourfold oscillations as a function of the field angle chi. The relationship between the node position and the oscillatory patterns shown by M-L and tau is clarified. It is also shown that the sign of the tau(chi)-oscillation does not change between H-c1 and H-c2, while the sign of the M-L(chi)-oscillation changes. The newly obtained result for tau indicates that the torque experiment can allow us to detect the in-plane anisotropies of H-c2 even in a material with strong fluctuations such as cuprate or organic superconductors, where the H-c2 itself cannot be determined experimentally.

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  • Comment on "Fluctuation-driven first-order transition in Pauli-limited d-wave superconductors" Reviewed

    R Ikeda, H Adachi

    PHYSICAL REVIEW LETTERS   95 ( 26 )   269703 - 269703   2005.12

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  • Mixed-state thermodynamics of superconductors with moderately large paramagnetic effects Reviewed

    H Adachi, M Ichioka, K Machida

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 8 )   2181 - 2184   2005.8

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    Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state, such as the specific heat C and magnetization M, are studied using the quasiclassical Eilenberger formalism. We demonstrate that with an increase of paramagnetic depairing effect, the sigh of the curvature of the field dependence of C changes from negative to positive, and that the Maki parameter kappa(2) becomes an increasing function of temperature. Our results provide a natural explanation for the unusual field dependence of C seen in CeCoIn5 in terms of the paramagnetic effect.

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  • Anisotropic diamagnetic response in type-II superconductors with gap and Fermi-surface anisotropies Reviewed

    H Adachi, P Miranovic, M Ichioka, K Machida

    PHYSICAL REVIEW LETTERS   94 ( 6 )   067007(1)-067007(4)   2005.2

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    The effects of anisotropic gap structures on a diamagnetic response are investigated in order to demonstrate that the field-angle-resolved magnetization [M-L (chi)] measurement can be used as a spectroscopic method to detect gap structures. Our microscopic calculation based on the quasiclassical Eilenberger formalism reveals that M-L (chi) in a superconductor with a fourfold gap displays a fourfold oscillation reflecting the gap and Fermi-surface anisotropies, and the sign of this oscillation changes at a field between H-c1 and H-c2. As a prototype of unconventional superconductors, magnetization data for borocarbides are also discussed.

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  • Modulated vortex lattice in high fields and gap nodes Reviewed

    Ryusuke Ikeda, Hiroto Adachi

    Physical Review B - Condensed Matter and Materials Physics   69 ( 21 )   1 - 212506   2004.6

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    The mean field vortex phase diagram of a quasi-two-dimensional superconductor with a nodal d-wave pairing and with strong Pauli spin depairing is studied in the parallel field case in order to examine the effect of gap nodes on the stability of a Fulde-Ferrell-Larkin-Ovchinnikov- (FFLO-) like vortex lattice. We find through a heuristic argument and a model calculation with a fourfold anisotropic Fermi surface that the FFLO-like state is relatively suppressed as the field approaches a nodal direction. When taking account of available experimental results together, the present result strongly suggests that the pairing symmetry of CeCoIn5 should be of dxy type.

    DOI: 10.1103/PhysRevB.69.212506

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  • Modulated vortex lattice in high fields and gap nodes Reviewed

    R Ikeda, H Adachi

    PHYSICAL REVIEW B   69 ( 21 )   212506(1)-212506(4)   2004.6

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    The mean field vortex phase diagram of a quasi-two-dimensional superconductor with a nodal d-wave pairing and with strong Pauli spin depairing is studied in the parallel field case in order to examine the effect of gap nodes on the stability of a Fulde-Ferrell-Larkin-Ovchinnikov- (FFLO-) like vortex lattice. We find through a heuristic argument and a model calculation with a fourfold anisotropic Fermi surface that the FFLO-like state is relatively suppressed as the field approaches a nodal direction. When taking account of available experimental results together, the present result strongly suggests that the pairing symmetry of CeCoIn5 should be of d(xy) type.

    DOI: 10.1103/PhysRevB.69.212506

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  • Effects of Pauli paramagnetism on the superconducting vortex phase diagram in strong fields Reviewed

    Hiroto Adachi, Ryusuke Ikeda

    Physical Review B - Condensed Matter and Materials Physics   68 ( 18 )   2003.11

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    The Ginzburg-Landau functional and the resultant phase diagram of quasi-two-dimensional superconductors in strong fields perpendicular to the layers, where the Pauli paramagnetic depairing is not negligible, are examined in detail by assuming the weak coupling BCS model with a dx2−y2-like pairing. It is found that the temperature at which the mean field (MF) transition at Hc2 changes into a discontinuous one lies much above another temperature at which a line HFFLO(T) of transition to a helical vortex solid similar to a Fulde-Ferrell-Larkin-Ovchinnikov state may begin to appear. In addition to MF results, details of a real phase diagram near the Hc2(T) line are examined based on a theoretical argument and Monte Carlo simulations, and it is found that the MF discontinuous transition is changed due to the fluctuation into a crossover which is nearly discontinuous in systems with weak enough fluctuation. These results are consistent both with the MF discontinuous behavior and a suggestion of HFFLO(T) in the heavy fermion superconductor CeCoIn5 with weak fluctuation and with their absence in cuprate and organic superconductors with strong fluctuation. © 2003 The American Physical Society.

    DOI: 10.1103/PhysRevB.68.184510

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  • Theoretical description of nearly discontinuous transition in superconductors with paramagnetic depairing Reviewed

    H Adachi, S Koikegami, R Ikeda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 10 )   2460 - 2463   2003.10

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    Based on a theoretical argument and Monte Carlo simulations of a Ginzburg-Landau model derived microscopically, it is argued that, in type-II superconductors where both the paramagnetic and orbital depairings are important, a strong first-order transition (FOT) at H-c2 expected in the mean field (MF) approximation never occurs in real systems and changes due to the fluctuation into a crossover. The present result explains why a nearly discontinuous crossover at H-c2 with no intrinsic hysteresis is observed only in a clean superconducting material with a singlet pairing and a high condensation energy such as CeCoIn5.

    DOI: 10.1143/JPSJ.72.2460

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  • Ginzburg-Landau functional for type-II superconductors with Pauli paramagnetic effect Reviewed

    H Adachi, R Ikeda

    JOURNAL OF PHYSICS-CONDENSED MATTER   15 ( 28 )   S2223 - S2226   2003.7

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    Effects of Pauli paramagnetism on type-II superconductivity are examined through a derivation of a Ginzburg-Landau (GL) functional by including the field-induced pair-breaking effects through the spin and orbital on an equal footing. On the basis of the resultant GL functional we discuss the corresponding high-field vortex phase diagram at the level of mean field approximation. Special attention is paid to the mutuality of characteristic temperatures, i.e., the temperatures: (1) at which the vortex state is described in terms of higher Landau levels; (2) at which a vortex state modulated along the field direction (a Fulde-Ferrell-Larkin-Ovchinnikov-like state) becomes stable; and (3) at which a superconducting transition becomes nearly discontinuous.

    DOI: 10.1088/0953-8984/15/28/356

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  • Theoretical study of phase transition in type II superconductors with Pauli paramagnetic effect in high magnetic field Reviewed

    H Adachi, R Ikeda

    PHYSICA B-CONDENSED MATTER   329   1391 - 1392   2003.5

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    High-field phase diagram of type II superconductors with paramagnetic depairing effect is examined through a theoretical argument and a numerical simulation of a Ginzburg-Landau model with a negative quartic term. Our results strongly suggest, contrary to the argument based on magnetization data in CeCoIn5, that the first-order transition at H-c2(T) in the mean field (MF) approximation is reflected in real systems merely as a crossover and that the thermal phase diagram is similar to that in the ordinary case where the MF transition is of second order. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0921-4526(02)02265-2

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  • Microscopic study of quantum vortex-glass transition field in two-dimensional superconductors Reviewed

    H Ishida, H Adachi, R Ikeda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   71 ( 1 )   245 - 253   2002.1

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    The position B-vg of a field-tuned superconductor-insulator quantum transition occuring in disordered thin films is examined within the mean field approximation and starting from a hamiltonian of BCS type (favoring the s-wave pairing) with a random potential, and effects of an electron-electron repulsion on the transition field B-vg are also considered. Our calculation shows that the (microscopic) disorder-induced reduction of B-vg suggested experimentally cannot be explained without taking account of the familiar interplay between the randomness and the electron-electron repulsion enhancing the quantum superconducting fluctuation in such systems.

    DOI: 10.1143/JPSJ.71.245

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  • Fluctuation conductivity in unconventional superconductors near critical disorder Reviewed

    H Adachi, R Ikeda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   70 ( 10 )   2848 - 2851   2001.10

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    The fluctuation conductivity sigma (s) in bulk superconductors with non s-wave pairing and with nonmagnetic disorder of strength D is studied at low T and within the Gaussian approximation. It is shown by assuming a quasi two-dimensional (M) electronic state that, only if the gap function d(mu)(p) is, as in a 2D p-wave pairing state, linear in the in-plane (relative) momentum p(perpendicular to), the inplane fluctuation conductivity on the line D = D-c is weakly divergent in low T limit, The present result may be useful in clarifying the true gap function of spin-triplet Sr2RuO4 through resistivity measurements.

    DOI: 10.1143/JPSJ.70.2848

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  • Josephson-vortex-glass transition in strong fields Reviewed

    R Ikeda, H Adachi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   69 ( 9 )   2993 - 3006   2000.9

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    A vortex-glass transition due to point disorder in Layered superconductors is studied for the case with an applied field parallel to the layers. Our calculation of tilt responses indicates that, irrespective of the magnitude of the field, the resulting glass phase, Josephson-vortex-glass (JG), should have a transverse Meissner effect, as in a planar splayed glass phase, only for a tilt perpendicular to the layers. Further, focusing on the high field (and/or high anisotropy) region B root Gamma &gt; phi(0)/d(2), where Gamma is the mass anisotropy in the Lawrence-Doniach model, the JG transition line T-JG(B) is shown to have a similar form to a B-T line following from the disorder-free Lindemann criterion and to decrease with increasing B root Gamma,in marked contrast to the disorder-free melting line insensitive to B root Gamma in such the high field region. This TJG(B) line seems to have been recently observed in a.c. susceptibility and in-plane resistivity measurements in BSCCO and qualitatively explains a field dependence at lower temperatures of previous BSCCO resistivity data showing the so-called in-plane Lorentz force-free behavior.

    DOI: 10.1143/JPSJ.69.2993

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  • Resistance peak under a magnetic field parallel to the conducting plane Reviewed

    E Ohmichi, H Adachi, Y Maeno, T Ishiguro, T Komatsu, G Saito

    SYNTHETIC METALS   103 ( 1-3 )   1912 - 1912   1999.6

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    Sharp magnetoresistance peak for the two-dimensional conductors, kappa-(BEDT-TTF)(2)Cu-2 (CN)(3) and Sr2RuO4, appearing under a field parallel to the conducting plane, were measured under 15 T at 1.5 K. The clear dependence with regard to the in-plane orientation is reported.

    DOI: 10.1016/S0379-6779(98)00619-5

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  • Angle-dependent magnetoresistance oscillation in the layered perovskite Sr2RuO4 Reviewed

    E Ohmichi, H Adachi, Y Mori, Y Maeno, T Ishiguro, T Oguchi

    PHYSICAL REVIEW B   59 ( 11 )   7263 - 7265   1999.3

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    The Fermi surface topology of the layered perovskite Sr2RuO4 was investigated through the observation of angle-dependent magnetoresistance oscillation under a magnetic field up to 17 T at 1.5 K. A series of angles giving the resistance peaks, observed under a constant field above 5 T, can be assigned to the Fermi wave-number vector of both the alpha and beta branches of the calculated Fermi surface. [S0163-1829(99)02511-4].

    DOI: 10.1103/PhysRevB.59.7263

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  • Local density of states in vortex states of nematic superconductors

    市岡優典, 上田貴裕, 安立裕人

    日本物理学会講演概要集(CD-ROM)   77 ( 1 )   2022

  • Vortex spin Hall effect and its experimental detection method

    平拓也, 加藤雄介, 市岡優典, 安立裕人

    日本物理学会講演概要集(CD-ROM)   76 ( 2 )   2021

  • Non-magnetic impurity effects in vortex states of nematic superconductors

    市岡優典, 世良泰明, 上田貴裕, 安立裕人

    日本物理学会講演概要集(CD-ROM)   76 ( 2 )   2021

  • Antiferromagnetic spin Seebeck effect near the Neel temperature Ⅱ

    Yamamoto Yutaka, Ichioka Masanori, Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   75.1   940 - 940   2020

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    DOI: 10.11316/jpsgaiyo.75.1.0_940

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  • Superconducting fluctuations and spin Hall effect

    Taira Takuya, Kato Yusuke, Ichioka Masanori, Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   75.1   1047 - 1047   2020

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    DOI: 10.11316/jpsgaiyo.75.1.0_1047

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  • Impurity Effect for Electron Structure in Vortex State

    Sera Yasuaki, Adachi Hiroto, Ichioka Masanori

    Meeting Abstracts of the Physical Society of Japan   75.1   1480 - 1480   2020

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    DOI: 10.11316/jpsgaiyo.75.1.0_1480

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  • Theory of spin pumping into spin-glass materials

    Fujimoto Yusei, Ichioka Masanori, Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   74.2   771 - 771   2019

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    DOI: 10.11316/jpsgaiyo.74.2.0_771

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  • Twofold Symmetric Electronic Structure of a Vortex in Type-II Superconductors

    Sera Yasuaki, Adachi Hiroto, Ichioka Masanori

    Meeting Abstracts of the Physical Society of Japan   74.2   1429 - 1429   2019

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    DOI: 10.11316/jpsgaiyo.74.2.0_1429

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  • Spin Seebeck effect in an antiferromagnet near neel point

    Yamamoto Yutaka, Ichioka Masanori, Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   74.1   1130 - 1130   2019

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    DOI: 10.11316/jpsgaiyo.74.1.0_1130

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  • Spin Seebeck effect in a ferromagnet near curie temperature

    Yamamoto Yutaka, Ichioka Masanori, Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   73.2   566 - 566   2018

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    DOI: 10.11316/jpsgaiyo.73.2.0_566

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  • Spin diffusion equation in superconductors : Analysis near Tc

    Taira Takuya

    Meeting Abstracts of the Physical Society of Japan   73.2   567 - 567   2018

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    DOI: 10.11316/jpsgaiyo.73.2.0_567

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  • Impurity effect and vortex core size in local electronic states around vortex

    Hashitani Yuki, Tanaka Kenta K., Adachi Hiroto, Ichioka Masanori

    Meeting Abstracts of the Physical Society of Japan   72.1   1629 - 1629   2017

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    DOI: 10.11316/jpsgaiyo.72.1.0_1629

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  • Theory of spin pumping into superconductors

    Inoue Masashi, Adachi Hiroto, Ichioka Masanori

    Meeting Abstracts of the Physical Society of Japan   72.1   1259 - 1259   2017

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    DOI: 10.11316/jpsgaiyo.72.1.0_1259

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  • Spin Seebeck effect in ferrimagnets

    大沼 悠一, 安立 裕人, 齊藤 英治, 前川 禎通

    社団法人日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan   209   29 - 34   2016.10

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  • 22aAD-2 Theory of the spin Seebeck effect

    Adachi Hiroto

    Meeting Abstracts of the Physical Society of Japan   70   1144 - 1145   2015

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    DOI: 10.11316/jpsgaiyo.70.1.0_1144

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  • 21aAD-7 Theory for thermal manipulation of spin pumping

    Ohnuma Y., Adachi H., Saitoh E., Maekawa S.

    Meeting Abstracts of the Physical Society of Japan   70   960 - 960   2015

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    DOI: 10.11316/jpsgaiyo.70.1.0_960

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  • 17aCG-2 Giant spin Seebeck effect in multilayer structures: Theory

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   70   854 - 854   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_854

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  • 17aCG-3 Two sign changes of spin Seebeck effect in compensated ferrimagnets

    Ohnuma Y., Adachi H., Saitoh E., Maekawa S.

    Meeting Abstracts of the Physical Society of Japan   70   855 - 855   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_855

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  • 7aBF-10 Theory of surface-plasmon-driven spin pumping

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   248 - 248   2014

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  • 7pPSA-10 Theory of spin pumping in a trilayer system

    Ohnuma Y, Adachi H, Saitoh E, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   275 - 275   2014

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  • 28pAF-4 Theoretical study of modulated ferromagnetic resonance relaxation due to the spin Seebeck effect II

    Ohnuma Y, Adachi H, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   516 - 516   2014

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  • 28pAF-5 Theory of unidirectional spin heat conveyer

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   516 - 516   2014

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  • Heat and Spin Currents

    193   15 - 20   2013.12

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  • 27pXG-6 Phonons and the spin Seebeck effect

    Adachi Hiroto

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   764 - 764   2013.3

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  • Theoretical consideration on the relationship between spin pumping & spin susceptibility

    Ohnuma Y, Adachi H, Saito E, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   68 ( 0 )   407 - 407   2013

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  • 26aPS-6 Theoretical study of modulated ferromagnetic resonance relaxation due to the spin Seebeck effect

    Ohnuma Y, Adachi H, Saitoh E, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   68 ( 0 )   499 - 499   2013

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  • Theory of acoustic spin pumping

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   68 ( 0 )   406 - 406   2013

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  • 24pBG-7 Theory of longitudinal spin-Seebeck effect

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   67 ( 0 )   506 - 506   2012

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  • 24pG-8 Theoretical study of spin-Seebeck effect with compensation effect

    Ohnuma Y, Adachi H, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   67 ( 0 )   506 - 506   2012

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  • 24pBG-5 Phonon-mediated spin Seebeck effect and acoustic spin pumping

    Uchida K, Adachi H, An T, Maekawa S, Saitoh E

    Meeting Abstracts of the Physical Society of Japan   67 ( 0 )   505 - 505   2012

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  • 19aCC-2 Theoretical study of ferrimagnetic spin Seebeck effect

    Ohnuma Y, Adachi H, Saitoh E, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   67 ( 0 )   411 - 411   2012

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  • 19aCC-1 Theory of efficiency of the spin-Seebeck Thermoelectric devices

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   67 ( 0 )   411 - 411   2012

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  • 25aHF-10 The role of phonons in the spin-Seebeck effects

    Uchida K, Adachi H, An T, Ota T, Maekawa S, Saitoh E

    Meeting Abstracts of the Physical Society of Japan   66 ( 0 )   456 - 456   2011

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  • 25aHF-1 Theory of longitudinal spin-Seebeck effect

    Adachi Hiroto, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   66 ( 0 )   454 - 454   2011

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  • New Interplay of Spin and Heat

    ADACHI H, MAEKAWA S

    Magnetics Japan   5 ( 6 )   256 - 263   2010.6

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  • 25aPS-37 Spin Seebeck effect in ferromagnetic insulators

    Takahashi S, Ohe J, Adachi H, Ieda J, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   65 ( 0 )   407 - 407   2010

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  • 24pWP-10 Numerical study on the thermally driven spin-wave spin current

    Ohe J, Adachi H, Takahashi S, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   65 ( 0 )   391 - 391   2010

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  • 22pGJ-10 Analysis of thermal spin current mediated by collective excitations II

    Adachi Hiroto, Takahashi Saburo, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   65 ( 0 )   487 - 487   2010

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  • 24pWP-9 Analysis of thermal spin current mediated by collective excitations III

    Adachi Hiroto, Takahashi Saburo, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   65 ( 0 )   391 - 391   2010

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  • 22pGJ-8 Spin injection into ferromagnetic insulators

    Takahashi S, Ohe J, Adachi H, Maekawa S

    Meeting Abstracts of the Physical Society of Japan   65 ( 0 )   487 - 487   2010

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  • 25aRK-4 How to detect the nematic phase in Sr3RU2O7

    Adachi Hiroto, Sigrist Manfred

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   408 - 408   2009.8

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  • 26aVD-5 Analysis of thermal spin current mediated by collective excitations

    Adachi Hiroto, Takahashi Saburo, Maekawa Sadamichi

    Meeting Abstracts of the Physical Society of Japan   64 ( 0 )   360 - 360   2009

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  • Zeeman effect and superconducting vortex states

    Solid state physics   42 ( 10 )   647 - 660   2007.10

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  • 20aXE-11 Stability of the FFLO state for the vortex-state

    Nakai N., Adachi H., Miranovic Predrag, Tsutsumi Y., Ichioka M., Machida K.

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   617 - 617   2007.2

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  • 25aZG-13 Quasiparticle thermal conductivity in a vortex state II

    Adachi H., Ichioka M., Machida K., Miranovic Predrag

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   487 - 487   2006.8

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  • 25pZG-7 Pauli paramagnetic effect and the form factor of neutron scattering in vortex state

    Ichioka M., Adachi H., Mizushima T., Machida K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   501 - 501   2006.8

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  • 30aUE-1 Electronic structure of FFLO vortex state in quasi-classical theory

    Ichioka M., Adachi H., Mizushima T., Machida K.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   646 - 646   2006.3

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  • 27aPS-9 Quasiparticle thermal conductivity in a vortex state

    Adachi H., Ichioka M., Machida K., Miranovic P.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   521 - 521   2006.3

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  • 22aYJ-6 Pauli paramagnetic effect and Knight shift in vortex state

    Ichioka M., Adachi H., Mizushima T., Machida K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   507 - 507   2005.8

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  • 19aYH-8 Anisotropic diamagnetic response in unvonventional superconductors II

    Adachi H., Ichioka M., Machida K., Miranovic P.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   365 - 365   2005.8

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  • 26pWM-10 Electronic state in a superconducting vortex phase near the Pauli limit

    Adachi H., Ichioka M., Machida K.

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   589 - 589   2005.3

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  • 14pRC-13 Anisotropic diamagnetic response in unvonventional superconductors

    Adachi H, Ichioka M, Machida K, Miranovic P

    Meeting abstracts of the Physical Society of Japan   59 ( 2 )   534 - 534   2004.8

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  • 30aXA-12 FFLO transiton and the pairing state II

    Adachi H, Ikeda R

    Meeting abstracts of the Physical Society of Japan   59 ( 1 )   635 - 635   2004.3

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  • FFLO and the pairing state

    Adachi H., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   58 ( 2 )   553 - 553   2003.8

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  • Phase Transition in Type II Superconductors with Pauli Paramagnetic Effect in High Magnetic Field II

    Adachi H., Koikegami S., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   58 ( 1 )   536 - 536   2003.3

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  • Theoretical Study of Vortex Phase Diagram of CeCoIn_5 :

    79 ( 6 )   1023 - 1023   2003

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  • Phase Transition in Type II Superconductors with Pauli Paramagnetic Effect in High Magnetic Field

    Adachi H., Koikegami S., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   57 ( 2 )   419 - 419   2002.8

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  • Microscopic Study of Quantum Vortex-Glass Transition Field in 2D Superconductor

    Ishida H., Adachi H., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   56 ( 2 )   671 - 671   2001.9

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  • Quantum Fluctuations in Disorderd Triplet Superconductors

    Adachi H., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   56 ( 1 )   545 - 545   2001.3

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  • Josephson-Vortex-Glass Transition

    Adachi H., Ikeda R.

    Meeting abstracts of the Physical Society of Japan   55 ( 1 )   438 - 438   2000.3

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  • Frequency mixing in quantum oscillations of Sr_2RuO_4

    OHMICHI E., ADACHI H., MORI Y., MAENO Y., ISHIGURO T.

    Meeting abstracts of the Physical Society of Japan   53 ( 2 )   703 - 703   1998.9

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  • Angle-dependent magnetoresistance oscillation of Sr_2RuO_4

    OHMICHI E., ADACHI H., MORI Y., MAENO Y., ISHIGURO T., OGUCHI T.

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   532 - 532   1998.3

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  • Low-Temperature Specific Heat of Layered Oxide Superconductor Sr_2RuO_4

    NISHIZAKI S., ADACHI H., MAENO E.

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   533 - 533   1998.3

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Presentations

  • Spin transport using antiferromagnetic magnons and superconducting vortices Invited

    Hiroto Adachi

    Spin Caloritronics XI, University of Illinois at Urbana-Champaign  2022 

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    Event date: 2022.5.23 - 2022.5.27

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  • Spin Seebeck/Pumping Effects near a Phase Transition Point Invited

    Hiroto Adachi

    Spin Caloritronics IX, The Ohio State University (Columbus)  2018 

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    Event date: 2018.6.24 - 2018.6.29

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  • Theory of spin pumping into superconductors Invited

    Hiroto Adachi

    New Excitations in Spintronics, Tohoku University (Sendai)  2018 

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    Event date: 2018.1.10 - 2018.1.14

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Research Projects

  • Theory of spin current phenomena utilizing the superconducting vortex as a real-space topological defect

    Grant number:22H01941  2022.04 - 2025.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

    安立 裕人, 大江 純一郎, 加藤 雄介, 市岡 優典

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    Grant amount:\8710000 ( Direct expense: \6700000 、 Indirect expense:\2010000 )

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  • トポロジカル磁性体のマグノンドラッグ効果を用いたスピン流熱電効果

    Grant number:21H01799  2021.04 - 2026.03

    日本学術振興会  科学研究費助成事業  基盤研究(B)

    大江 純一郎, 河野 浩, 安立 裕人, 大槻 東巳

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    Grant amount:\13260000 ( Direct expense: \10200000 、 Indirect expense:\3060000 )

    非一様な磁化構造を有する磁性体中の熱電効果について、理論的研究を行った。特に、磁性体中の集団励起であるマグノンが誘起する電流、スピン流について解析的、数値計算の両面から研究を行った。非一様な磁化構造として、結晶の反転対称性の欠如によるジャロシンスキー・守谷相互作用によるねじれた磁化構造に注目した。1次元的な螺旋構造や、2次元的なスカーミオン構造がある系に温度勾配を印加した場合、系に誘起される非平衡マグノン分布を数値計算により明らかにした。また、このマグノンにより熱電効果の増強や、スピン流が誘起されることを明らかにした。分担者の大槻は、開放系などの非エルミート系の対称性をエルミート系で議論できることに着目し,非エルミート系のアンダーソン局在の臨界指数がエルミート系に対応づけられることを示した。量子マグノンを記述するシュレーディンガー方程式は非エルミートとなり,上述よりこれもエルミート系に対応づけた。これより量子マグノンホール効果が量子ホール効果と等価であることを示した。また,量子ダイナミクスをlong-short term memory networkというタイプのニューラルネットワークで解析できることを示した。分担者の河野は、反強磁性体のスピン移行トルクとその散逸補正(α項)、減衰トルク(β項)の微視的計算を行った。強磁性体との類似点・相違点に注意して整理する一方で、反強磁性体では2種類のスピン移行トルクが存在すること、スピン波のドップラーシフトには両方が同じ程度寄与することを示した。伝導電子のホッピングを調節することにより、反強磁性のトルクと強磁性のトルクを連続的につなげて議論した。

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  • 超伝導渦糸フローが生み出す新しいスピン流の理論的探求

    Grant number:19K05253  2019.04 - 2023.03

    日本学術振興会  科学研究費助成事業  基盤研究(C)

    安立 裕人, 大江 純一郎

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    Grant amount:\3640000 ( Direct expense: \2800000 、 Indirect expense:\840000 )

    まず、令和3年度の研究開始直後に、令和2年度に進めていた研究成果、具体的には渦糸スピンホール効果によるスピンホール伝導度の微視的計算結果を、T. Taira et al., "Spin Hall effect generated by fluctuating vortices in type-II superconductors", Phys. Rev. B 103, 134417 (2021)] にて無事出版した。これにより、本研究課題の柱の1つが完了したことになる。
    これを受け、令和3年度はもう1つの柱である、渦糸スピンホール効果の数値シミュレーションに着手した。その結果、この研究テーマでは渦糸多体系の実時間ダイナミクスを直接相手にしなければならない一方で、現在我々のグループで保有している数値計算資源はまだまだ非力であることが判明した。そのため、昨年度の研究テーマは、より小規模な数値シミュレーションで現象の本質に迫れる、反強磁性スピンゼーベック効果の数値シミュレーションへと研究方向をシフトした。
    新たなターゲットとしたスピンホール効果とは、熱エネルギーからスピン流を作り出す現象であり、特に近年、自発磁化を持たない反強磁性体のスピンゼーベック効果が大きな注目を集めている。我々は、Cr2O3という反強磁性体の高磁場で観測された、スピンフロップ転移に伴うスピンゼーベック効果の符号反転に着目した。そして、時間依存ギンツブルグ・ランダウ方程式のシミュレーションにより、磁性体/非磁性電極の界面で通常の磁気的交換相互作用が働く場合には信号の符号反転は生じない一方、交換バイアス効果に類似の交換相互作用(ネールベクトルと伝導電子スピンが結合する交換相互作用)が界面で働く場合には、信号が符号反転することを明らかとした。

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  • Theoretical research for microscopic understanding and visualization of the spin Seebeck effect

    Grant number:15K05151  2015.04 - 2019.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

    ADACHI Hiroto

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    Grant amount:\3120000 ( Direct expense: \2400000 、 Indirect expense:\720000 )

    Spin Seebeck effect refers to the generation of spin current by a heat current applied to a magnet. In this project, we have theoretically investigated the spin Seebeck effect near the magnetic phase transition point. By means of a model calculation using a time-dependent Ginzburg-Landau equation, we have shown that in both ferromagnets and antiferromagnets, the spin Seebeck effect signal is proportional to the magnetization in the sample.

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  • Development of new spin utilization technology led by Spin Berry Phase

    Grant number:26247063  2014.04 - 2017.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (A)

    Maekawa Sadamichi, YASUOKA Hiroshi, SAITOH Eiji

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    Grant amount:\33800000 ( Direct expense: \26000000 、 Indirect expense:\7800000 )

    We performed theoretical researches of novel voltage generation methods using the spin Berry phase and observation of the spin Berry phase accumulation in the nuclear spin system on the rotating frame by the nuclear magnetic resonance method. We show that the spinmotive force is enhanced by collective motion of bubble magnetic domains using numerical calculation, and show theoretically that spinmotive force is also generated by domain wall motion in antiferromagnets. In the nuclear spin system we observed the effective magnetic field induced by rotation (Barnett field) and crossover behavior between the Berry phase and the Barnett field.

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  • Research on the thermal spin current generation

    Grant number:22740210  2010.04 - 2014.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (B)

    ADACHI Hiroto

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    Grant amount:\2730000 ( Direct expense: \2100000 、 Indirect expense:\630000 )

    The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an adjacent nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. The basic mechanism of the spin Seebeck effect has been theoretically investigated in this project, and it has been shown that non-equilibrium magnons and phonons play crucial roles in the spin Seebeck effect.

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  • Controlled electronic phases of transition metal oxides

    Grant number:19204035  2007 - 2010

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (A)

    MAEKAWA Sadamichi, MORI Michiyasu, IEDA Junichi, ADACHI Hiroto, OHE Junichiro, KUBO Katsunori, ONISHI Hiroaki, KOSHIBAE Wataru

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    Grant amount:\38350000 ( Direct expense: \29500000 、 Indirect expense:\8850000 )

    In the strongly correlated electron systems, various electronic phases such as superconductivity and ferromagnetism are competed. This study aims to understand such competing electronic phases in the correlated electron systems by use of numerical techniques. Magnetic semiconductors show some unique properties by a coupling between conduction electrons and magnetic ions. Due to this coupling, one needs to consider simultaneously the electronic states of semiconductors and the electrons correlation inducing the magnetism. In this study, we combine the density functional theory for the electronic states of semiconductors and the quantum Monte Carlo method to include the correlation effects of magnetic ions. Furthermore, the thermoelectric power in the correlated electron systems is clarified by the dynamical mean-field theory.

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  • Spin current and electromotive force due to domain wall motion

    Grant number:19048009  2007 - 2010

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Priority Areas

    MAEKAWA Sadamichi, MORI Michiyasu, IEDA Junichi, ADACHI Hiroto, TAKAHASHI Saburo, OHE Junichiro

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    Grant amount:\13400000 ( Direct expense: \13400000 )

    The aims of this study are to establish the quantum mechanical basis for "spinmotive force," a new mechanism of generating an electric voltage by domain wall dynamics, and to propose new concepts in magnetic devices based on this effect. We developed numerical algorisms for calculating the spinmotive force in arbitrary magnetic nanostructures and clarified the relationship between magnetization dynamics and induced spinmotive force. We analyzed spinmotive forces induced by a gyrating magnetic vortex, domain wall motion in a nonuniform nanowire, and ferromagnetic resonance in an asymmetric magnetic thin film. We also proposed a new concept of a magnetic read-head based on the spinmotive force.

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  • 強相関電子系物質で見られる新しい超伝導状態の理論的研究

    Grant number:18740205  2006 - 2007

    日本学術振興会  科学研究費助成事業  若手研究(B)

    安立 裕人

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    Grant amount:\1400000 ( Direct expense: \1400000 )

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