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Hideaki Sakai

Section

Institute for Materials Research

Job title

Professor

Degree

researchmap

https://researchmap.jp/7000018618

J-GLOBAL ID

201601014889087646

e-Rad No.

20534598

Researcher ID

G-1008-2014

Research History 12

2025/10 - Present

Tohoku University　Institute for Materials Research
2015/04 - 2025/09

Osaka University　Graduate School of Science, Department of Physics
2023/08 - 2024/01

マックスプランク固体化学物理学研究所　客員研究員（兼任）
2022/04 - 2023/03

東北大学金属材料研究所　委嘱准教授（兼任）
2016/10 - 2020/03

Japan Science and Technology Agency
2016/04 - 2016/09

The University of Tokyo　The Institute for Solid State Physics
2011/10 - 2015/03

The University of Tokyo　The Graduate School of Engineering, Department of Applied Physics
2010/07 - 2011/10

セントアンドリュース大学　物理・天文学科　リサーチフェロー
2010/07 - 2011/06

キャノンファンデーションヨーロッパ　リサーチフェロー（兼任）
2008/10 - 2010/06

理化学研究所　交差相関物質研究チーム　基礎科学特別研究員
2007/04 - 2008/09

日本学術振興会　特別研究員DC2
2003/04 - 2005/09

日本電信電話株式会社　マイクロシステムインテグレーション研究所　社員

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Education 3

東京大学大学院　工学系研究科　物理工学専攻（博士課程）

2005/10 - 2008/09
東京大学大学院　理学系研究科　物理学専攻（修士課程）

2001/04 - 2003/03
The University of Tokyo　Faculty of Science　Department of Physics

1997/04 - 2001/03

Research Interests 8

磁気熱量効果
巨大磁気抵抗効果
マルチフェロイクス
quantum transport
高圧合成
thermoelectricity
Dirac fermion systems
strongly correlated electron systems

Research Areas 2

Nanotechnology/Materials / Applied materials /
Natural sciences / Magnetism, superconductivity, and strongly correlated systems /

Awards 3

Reviewer of the Month

2023/02　Communications Materials (Nature Portfolio)　Outstanding Referee
第1回フロンティア奨励賞

2019/11　強磁場フォーラム
大阪大学賞

2018/11　大阪大学

Papers 81

Lattice softening and diffusive dynamics in the polar metal LiReO ₃ International-coauthorship Peer-reviewed

Kantaro Murayama, Ryota Masuki, Cédric Tassel, Hideaki Sakai, Tatsuya Yanagisawa, Keito Yoshida, Hiroshi Oike, Suguru Yoshida, Xiangyu Gu, Kohdai Ishida, Morito Namba, Ksenia Denisova, Valérie Dupray, Simon Clevers, Olivier Mentré, Takuya Nomoto, Terumasa Tadano, Craig M. Brown, Peter Lemmens, Ryotaro Arita, Hiroshi Takatsu, Hiroshi Kageyama

Science Advances　12　(14)　2026/04/03
Publisher: American Association for the Advancement of Science (AAAS)
DOI： 10.1126/sciadv.adt3886 　

eISSN： 2375-2548

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Polar metals, characterized by the nontrivial coexistence of metallicity and polar structural order, define an emerging frontier in quantum materials research. However, the interplay between their structural phase transitions and fluctuation dynamics remains poorly understood. Here, we reveal distinct diffusive dynamics in metallic lithium rhenium trioxide (LiReO ₃ ) associated with its polar-to-nonpolar transition. Unlike isostructural lithium niobate (LiOsO ₃ ) and related systems, LiReO ₃ exhibits pronounced phase fluctuations both above and below T _s . Thermoelectric, Raman, and ultrasound measurements demonstrate a probe-dependent thermal hysteresis, while ultrasound data further show lattice softening and persistent resonant absorption at low temperatures across a broad timescale (1 to 100 microseconds). These observations indicate a multiscale spatiotemporal dynamics governed by a shallow anharmonic potential stabilized by itinerant electrons, as supported by finite-temperature first-principles calculations. By mapping the fluctuation landscape shaped by itinerant electrons, this work offers a previously unexplored perspective for exploiting fluctuation-driven phenomena in polar metals.
Impact of the out-of-plane conductivity on spin transport evaluation in a van der Waals material International-journal Peer-reviewed

Ryoya Nakamura, Futo Tokuda, Yoshinobu Ono, Nan Jiang, Hideaki Sakai, Masayuki Ochi, Hiroaki Ishizuka, Yasuhiro Niimi

Physical Review B　113　(10)　2026/03/03
Publisher: American Physical Society (APS)
DOI： 10.1103/kddr-3jj6 　

ISSN： 2469-9950

eISSN： 2469-9969
High-field transport in SrCdBi<sub>2</sub> with a 2D Bi layer International-journal Peer-reviewed

H. Sakai, K. Tanaka, M. Kondo, M. Tokunaga, A. Yamashita, H. Murakawa, N. Hanasaki

JJAP Conference Proceedings　12　011007-011007　2026/02
Publisher: The Japan Society of Applied Physics
DOI： 10.56646/jjapcp.12.0_011007 　

eISSN： 2758-2450
Transport evidence of current-induced nematic Dirac valleys in a parity-time-symmetric antiferromagnet Peer-reviewed

Hideaki Sakai, Yuya Miyamoto, Motoi Kimata, Hikaru Watanabe, Yoichi Yanase, Masayuki Ochi, Masaki Kondo, Hiroshi Murakawa, Noriaki Hanasaki

Nature Communications　16　(1)　2026/01/07
Publisher: Springer Science and Business Media LLC
DOI： 10.1038/s41467-025-67229-y 　

eISSN： 2041-1723
Frustrated random-singlet state with ice-type structural fluctuation in spinel titanates Peer-reviewed

Noriaki Hanasaki, Takayuki Hattori, Takumi Komoda, Kouei Minamoto, Shuhei Torigoe, Satoshi Yamashita, Yasuhiro Nakazawa, Takehiko Nakano, Kouhei Yoshimi, Mitsuharu Yashima, Hidekazu Mukuda, Utami Widyaiswari, Isao Watanabe, Akihiro Koda, Takashi Honda, Toshiya Otomo, Hajime Sagayama, Katsuaki Kodama, Hiroshi Murakawa, Hideaki Sakai

Proceedings of the National Academy of Sciences　123　(1)　2025/12/30
Publisher: Proceedings of the National Academy of Sciences
DOI： 10.1073/pnas.2517926123 　

ISSN： 0027-8424

eISSN： 1091-6490

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In ice, it is well known that the orientation of H ₂ O molecules is disordered by geometrical frustration. Ice-analogous materials having a pyrochlore lattice display interesting phenomena such as the spin-ice state and the magnetic monopole. In the spinel titanate MgTi ₂ O ₄ , the Ti ions have a quantum spin in the pyrochlore lattice. The Ti ions are displaced, accompanied by the spin-singlet formation. Since this displacement pattern follows the ice rule, the title compound is a material analogous to ice. When a small quantity of Ti ions are replaced with Mg ions, the ice-type structural fluctuation exists. In this structural ice-type state, the spins are also fluctuating at a nanosecond scale down to 0.3 K. We ascribed this phenomenon to the gapless frustrated random-singlet state, in which the spin-singlet pairs are resonating, and the orphan spins are hopping.
Observation of Zeeman splitting in the spin-polarized chiral fermion state in the Weyl semimetal TaAs Peer-reviewed

H. Murakawa, M. Komada, D.-A. Deaconu, M. S. Bahramy, R. V. Belosludov, T. Kida, M. Hagiwara, H. Sakai, N. Hanasaki

Physical Review B　112　(4)　2025/07/10
Publisher: American Physical Society (APS)
DOI： 10.1103/qjt5-x6p4 　

ISSN： 2469-9950

eISSN： 2469-9969
Anomalous Hall and Nernst effect and thermoelectric performance of Sb-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>MnB</mml:mi><mml:msub><mml:mi mathvariant="normal">i</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:mi mathvariant="normal">T</mml:mi><mml:msub><mml:mi mathvariant="normal">e</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:mrow></mml:math> International-journal International-coauthorship Peer-reviewed

Xinmeng Hu, Takayoshi Katase, Masaki Kondo, Noriaki Hanasaki, Hideaki Sakai, Jiazhen Wu

Physical Review Materials　9　(1)　015403-015403　2025/01/27
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevmaterials.9.015403 　

eISSN： 2475-9953
Nonreciprocal charge transport in polar Dirac metals with tunable spin-valley coupling Peer-reviewed

M. Kondo, M. Kimata, M. Ochi, T. Kaneko, K. Kuroki, K. Sudo, S. Sakaguchi, H. Murakawa, N. Hanasaki, H. Sakai

Physical Review Research　7　(1)　2025/01/10
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevresearch.7.013041 　

eISSN： 2643-1564

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Nonreciprocal charge transport in solids, where resistance is different between rightward and leftward currents, is a key function of rectifying devices in modern electronics, as exemplified by p−n semiconductor junctions. Recently, this was also demonstrated in noncentrosymmetric materials in magnetic fields since their band structure exhibits spin polarization coupled to the position of momentum space due to antisymmetric spin-orbit coupling. To enhance the magnitude of the nonreciprocal effect, it is essential to tune such spin-momentum coupling, which has been hampered in conventional materials owing to the difficulty in controlling the broken inversion symmetry built into the lattice and interfacial structures. Here, we report large nonreciprocal resistivity in the layered polar metal BaMnX2 (X=Sb, Bi), where the spin-polarized Dirac dispersion depends on the in-plane polarization tunable by chemical substitution of the X site. For X=Sb with a pair of single-type valleys, the nonreciprocal resistivity increases monotonically with decreasing temperature, while for X=Bi with multiple types of valleys it is reduced by about an order of magnitude and exhibits a peak at a low temperature. Theoretical calculations indicate that the nonreciprocal resistivity is sensitive not only to the spin-momentum (spin-valley) coupling but also to the Fermi energy and the Dirac dispersion. The observed significant variation of nonreciprocal transport in the same series of materials might be of great use in the design of junction-free rectifying devices and circuits. Published by the American Physical Society 2025
Local structural disorder introduced by Cr in fcc high-/medium-entropy alloys consisting of 3d transition metal elements

D. Furuya, M. Oda, Z. Chen, L. Li, H. Murakawa, H. Sakai, H. Nitani, Y. Niwa, H. Abe, H. Uetsuka, T. Karube, H. Inui, N. Hanasaki

Applied Physics Letters　125　(20)　2024/11/11
Publisher: AIP Publishing
DOI： 10.1063/5.0231343 　

ISSN： 0003-6951

eISSN： 1077-3118

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High-/medium-entropy alloys (H/MEAs) have attracted attention for their excellent mechanical properties. According to first-principles calculations, the atomic displacements from their lattice points are element-dependent and correlated with the yield strength of H/MEAs. To investigate experimentally the element dependence of the local structure, we measured the extended x-ray absorption fine structure in seven kinds of face-centered cubic H/MEAs consisting of 3d transition metal elements. Our experimental results indicate that the local disorder around chromium (Cr) is larger than that around other elements, which is a common feature in all the measured fcc H/MEAs, aligning with prior theoretical studies indicating larger displacements of Cr in comparison to other elements. We discuss the mechanism underlying the local structural disorder induced by the constituent element Cr.
Large nonlinear optical magnetoelectric response in a noncentrosymmetric magnetic Weyl semimetal Peer-reviewed

Kentaro Shoriki, Keigo Moriishi, Yoshihiro Okamura, Kohei Yokoi, Hidetomo Usui, Hiroshi Murakawa, Hideaki Sakai, Noriaki Hanasaki, Yoshinori Tokura, Youtarou Takahashi

Proceedings of the National Academy of Sciences　121　(12)　2024/03/14
Publisher: Proceedings of the National Academy of Sciences
DOI： 10.1073/pnas.2316910121 　

ISSN： 0027-8424

eISSN： 1091-6490

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Weyl semimetals resulting from either inversion ( P ) or time-reversal ( T ) symmetry breaking have been revealed to show the record-breaking large optical response due to intense Berry curvature of Weyl-node pairs. Different classes of Weyl semimetals with both P and T symmetry breaking potentially exhibit optical magnetoelectric (ME) responses, which are essentially distinct from the previously observed optical responses in conventional Weyl semimetals, leading to the versatile functions such as directional dependence for light propagation and gyrotropic effects. However, such optical ME phenomena of (semi)metallic systems have remained elusive so far. Here, we show the large nonlinear optical ME response in noncentrosymmetric magnetic Weyl semimetal PrAlGe, in which the polar structural asymmetry and ferromagnetic ordering break P and T symmetry. We observe the giant second harmonic generation (SHG) arising from the P symmetry breaking in the paramagnetic phase, being comparable to the largest SHG response reported in Weyl semimetal TaAs. In the ferromagnetically ordered phase, it is found that interference between this nonmagnetic SHG and the magnetically induced SHG emerging due to both P and T symmetry breaking results in the magnetic field switching of SHG intensity. Furthermore, such an interference effect critically depends on the light-propagating direction. The corresponding magnetically induced nonlinear susceptibility is significantly larger than the prototypical ME material, manifesting the existence of the strong nonlinear dynamical ME coupling. The present findings establish the unique optical functionality of P - and T -symmetry broken ME topological semimetals.
Ferrimagnetic charge order in molecular conductors with diluted localized spins exhibiting enhanced giant magnetoresistance effect Peer-reviewed

Ryuta Ishii, Misato Uejo, Erina Watari, Mitsuo Ikeda, Hiroshi Murakawa, Hideaki Sakai, Masaki Matsuda, Hideo Yoshioka, Masahisa Tsuchiizu, Noriaki Hanasaki

Physical Review B　108　(20)　2023/11/09
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.108.205114 　

ISSN： 2469-9950

eISSN： 2469-9969
Variation of Landau level splitting in the Fermi level controlled Dirac metals (Eu,Gd) MnBi₂ International-journal Peer-reviewed

H. Sakai, K. Nakagawa, K. Tsuruda, J. Shiogai, K. Akiba, M. Tokunaga, S. Kimura, S. Awaji, A. Tsukazaki, H. Murakawa, N. Hanasaki

Physical Review B　108　(11)　115142-1-115142-7　2023/09/21
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.108.115142 　

ISSN： 2469-9950

eISSN： 2469-9969
Giant negative magnetoresistance in the layered semiconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CeTe</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Sb</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math> with variable magnetic polaron density Peer-reviewed

H. Murakawa, Y. Nakaoka, K. Iwase, T. Kida, M. Hagiwara, H. Sakai, N. Hanasaki

Physical Review B　107　(16)　2023/04/24
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.107.165138 　

ISSN： 2469-9950

eISSN： 2469-9969
Field-tunable Weyl points and large anomalous Hall effect in the degenerate magnetic semiconductor EuMg2Bi2 Peer-reviewed

M. Kondo, M. Ochi, R. Kurihara, A. Miyake, Y. Yamasaki, M. Tokunaga, H. Nakao, K. Kuroki, T. Kida, M. Hagiwara, H. Murakawa, N. Hanasaki, H. Sakai

Physical Review B　107　(12)　L121112　2023/03
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevB.107.L121112 　

ISSN： 2469-9950

eISSN： 2469-9969
High-field Studies on Layered Magnetic and Polar Dirac Metals: Novel Quantum Transport Phenomena Coupled with Spin-valley Degrees of Freedom Invited Peer-reviewed

Hideaki Sakai

Journal of the Physical Society of Japan　91　(10)　101001-101001　2022/10/15
Publisher: Physical Society of Japan
DOI： 10.7566/JPSJ.91.101001 　

ISSN： 0031-9015

eISSN： 1347-4073
Anomalous Nernst effect in the nonmagnetic nodal-line semimetal PbTaSe2 Peer-reviewed

Kohei Yokoi, Hiroshi Murakawa, Hideaki Sakai, Noriaki Hanasaki

Physical Review B　106　(11)　2022/09/12
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevB.106.115118 　

ISSN： 2469-9950

eISSN： 2469-9969
In-plane anisotropic charge dynamics in the layered polar Dirac semimetal BaMnSb2 Peer-reviewed

H. Yoshizawa, H. Sakai, M. Kondo, M. Ochi, K. Kuroki, N. Hanasaki, J. Fujioka

Physical Review B　105　(24)　L241110　2022/06/15
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.105.l241110 　

ISSN： 2469-9950

eISSN： 2469-9969
Giant anisotropic magnetoresistance at low magnetic fields in a layered semiconductor International-journal Peer-reviewed

H. Murakawa, Y. Nakaoka, T. Kida, M. Hagiwara, H. Sakai, N. Hanasaki

Physical Review Materials　6　(5)　054604　2022/05/31
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevMaterials.6.054604 　

eISSN： 2475-9953
Magnetic Generation and Switching of Topological Quantum Phases in a Trivial Semimetal α−EuP3 Peer-reviewed

Alex Hiro Mayo, Hidefumi Takahashi, Mohammad Saeed Bahramy, Atsuro Nomoto, Hideaki Sakai, Shintaro Ishiwata

Physical Review X　12　(1)　011033　2022/02/18
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevx.12.011033 　

eISSN： 2160-3308
Element dependence of local disorder in medium-entropy alloy CrCoNi International-journal Peer-reviewed

N. Hanasaki, M. Oda, K. Niitsu, K. Ehara, H. Murakawa, H. Sakai, H. Nitani, H. Abe, H. Sagayama, H. Uetsuka, T. Karube, H. Inui

AIP Advances　11　(12)　125216-125216　2021/12/01
Publisher: AIP Publishing
DOI： 10.1063/5.0072766 　

eISSN： 2158-3226
ブロック層を利用した多彩なディラック電子系物質の開拓ー磁性・極性とのカップリング Invited Peer-reviewed

酒井英明

日本物理学会誌（最近の研究から）　76　(11)　729-734　2021/11

DOI： 10.11316/butsuri.76.11_729 　
Dirac Loops in a Strongly Correlated Metal: Origin of Large Magnetoresistance? Invited

Hideaki Sakai

JPSJ News and Comments　18　14　2021/10/22
Publisher: Physical Society of Japan
DOI： 10.7566/JPSJNC.18.14 　

ISSN： 2188-076X
Variation of charge dynamics upon antiferromagnetic transitions in the Dirac semimetal EuMnBi2 International-journal Peer-reviewed

H. Nishiyama, H. Sakai, K. Nakagawa, N. Hanasaki, S. Ishiwata, H. Masuda, M. Ochi, K. Kuroki, S. Iguchi, T. Sasaki, Y. Ikemoto, T. Moriwaki, K. Ueda, Y. Tokura, J. Fujioka

Physical Review B　104　(11)　115111　2021/09/07
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevB.104.115111 　

ISSN： 2469-9950

eISSN： 2469-9969
Tunable spin-valley coupling in layered polar Dirac metals Peer-reviewed

Masaki Kondo, Masayuki Ochi, Tatsuhiro Kojima, Ryosuke Kurihara, Daiki Sekine, Masakazu Matsubara, Atsushi Miyake, Masashi Tokunaga, Kazuhiko Kuroki, Hiroshi Murakawa, Noriaki Hanasaki, Hideaki Sakai

Communications Materials　2　(1)　49　2021/05/14

DOI： 10.1038/s43246-021-00152-z 　

eISSN： 2662-4443
Enhancing Thermopower and Nernst Signal of High‐Mobility Dirac Carriers by Fermi Level Tuning in the Layered Magnet EuMnBi 2 International-journal Peer-reviewed

Keigo Tsuruda, Kento Nakagawa, Masayuki Ochi, Kazuhiko Kuroki, Masashi Tokunaga, Hiroshi Murakawa, Noriaki Hanasaki, Hideaki Sakai

Advanced Functional Materials　31　(29)　2102275　2021/05/06

DOI： 10.1002/adfm.202102275 　

ISSN： 1616-301X

eISSN： 1616-3028
Optimizations of the Sintering Temperature to Reduce the Nd₃RuO₇Phase and Investigations of their Effect on the Magnetic Properties in Nd₂Ru₂O₇ Peer-reviewed

Hideaki Sakai

Thermec: International Conference on Processing and Manufacturing of Advanced Materials　1028　3-8　2021/04
Publisher: Trans Tech Publications, Ltd.
DOI： 10.4028/WWW.SCIENTIFIC.NET/MSF.1028.3 　

eISSN： 1662-9752

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One of the pyrochlore systems, Nd₂Ru₂O₇, shows unique magnetic properties and can be a candidate of the electrocatalyst material for industrial applications. This system shows magnetic anomalies around 1.8 K, 21 K, and 146 K. The anomaly at 21 K is suggested to be coming from the impurity component of Nd₃RuO₇ and is still debatable. To investigate the effects of impurities on the magnetic properties of this sample, we synthesized some samples (labelled as Sample-I and II) using the solid-state reaction method with different heat treatment conditions and measured the magnetic susceptibility. We found that low sintering temperatures generated impurity phases of raw materials and Nd₃RuO₇. We also confirmed that those impurity phases were able to be reduced by optimizing heat treatment conditions. The optimum temperature for the sintering process should not be higher than 1000°C. The higher sintering temperatures yield more Nd₃RuO₇ impurity phases. Magnetic susceptibility measurements showed that samples with Nd₃RuO₇ impurity phases exhibited a peak around 21 K in the zero field-cooled condition accompanied by a broad peak around 12 K in the field-cooled condition indicating the appearance of Nd₃RuO₇.
Ta-181 nuclear quadrupole resonance study of the noncentrosymmetric superconductor PbTaSe2 Peer-reviewed

Hideaki Sakai

Physical Review B　102　(21)　214504　2020/12/10

DOI： 10.1103/PHYSREVB.102.214504 　

ISSN： 2469-9950

eISSN： 2469-9969
Switching of band inversion and topological surface states by charge density wave Peer-reviewed

N. Mitsuishi, Y. Sugita, M. S. Bahramy, M. Kamitani, T. Sonobe, M. Sakano, T. Shimojima, H. Takahashi, H. Sakai, K. Horiba, H. Kumigashira, K. Taguchi, K. Miyamoto, T. Okuda, S. Ishiwata, Y. Motome, K. Ishizaka

Nature Communications　11　(1)　2466　2020/12
Publisher: Springer Science and Business Media LLC
DOI： 10.1038/s41467-020-16290-w 　

eISSN： 2041-1723

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Abstract Topologically nontrivial materials host protected edge states associated with the bulk band inversion through the bulk-edge correspondence. Manipulating such edge states is highly desired for developing new functions and devices practically using their dissipation-less nature and spin-momentum locking. Here we introduce a transition-metal dichalcogenide VTe₂, that hosts a charge density wave (CDW) coupled with the band inversion involving V3d and Te5p orbitals. Spin- and angle-resolved photoemission spectroscopy with first-principles calculations reveal the huge anisotropic modification of the bulk electronic structure by the CDW formation, accompanying the selective disappearance of Dirac-type spin-polarized topological surface states that exist in the normal state. Thorough three dimensional investigation of bulk states indicates that the corresponding band inversion at the Brillouin zone boundary dissolves upon the CDW formation, by transforming into anomalous flat bands. Our finding provides a new insight to the topological manipulation of matters by utilizing CDWs’ flexible characters to external stimuli.
Magnetic Properties of Pyrochlore Ruthenate Nd₂Ru₂O₇ Studied by μSR Peer-reviewed

Utami Widyaiswari, Hideaki Sakai, Kanji Inoue, Noriaki Hanasaki, Dita Puspita Sari, Budhy Kurniawan, Isao Watanabe

Key Engineering Materials　860　288-293　2020/08
Publisher: Trans Tech Publications, Ltd.
DOI： 10.4028/www.scientific.net/kem.860.288 　

eISSN： 1662-9795

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We investigated the magnetic properties of pyrochlore ruthenates, <italic>R</italic>₂Ru₂O₇, by using the muon spin relaxation (μSR) method. The appearance of a magnetically ordered state was confirmed below 145 K by observing the decrease in the initial asymmetry of the muon-spin polarization. This was due to a long-range ordering of Ru⁴⁺ spins. An additional anomaly in the μSR time spectrum was observed around 30 K. A part of the lost initial asymmetry was recovered and gradually decreases again with decreasing temperature below 30 K. This anomaly was supposed to be due to a magnetic ordering of Nd³⁺ spins which was coupled with ordered Ir moment via the 3<italic>d</italic>-4<italic>f</italic> exchange interaction.
Ferroelectric atomic displacement in multiferroic tetragonal perovskite Sr1/2Ba1/2MnO3 Peer-reviewed

D. Okuyama, K. Yamauchi, H. Sakai, Y. Taguchi, Y. Tokura, K. Sugimoto, T. J. Sato, T. Oguchi

Physical Review Research　2　(3)　033038　2020/07/08
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevresearch.2.033038 　

eISSN： 2643-1564
Nanoscale Imaging of Unusual Photoacoustic Waves in Thin Flake VTe2 Peer-reviewed

Asuka Nakamura, Takahiro Shimojima, Yusuke Chiashi, Manabu Kamitani, Hideaki Sakai, Shintaro Ishiwata, Han Li, Kyoko Ishizaka

Nano Letters　20　(7)　4932-4938　2020/06/09
Publisher: American Chemical Society (ACS)
DOI： 10.1021/acs.nanolett.0c01006 　

ISSN： 1530-6984

eISSN： 1530-6992
Field-induced spin reorientation in the antiferromagnetic Dirac material EuMnBi2 revealed by neutron and resonant x-ray diffraction Peer-reviewed

H. Masuda, H. Sakai, H. Takahashi, Y. Yamasaki, A. Nakao, T. Moyoshi, H. Nakao, Y. Murakami, T. Arima, S. Ishiwata

Physical Review B　101　(17)　174411　2020/05/06
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.101.174411 　

ISSN： 2469-9950

eISSN： 2469-9969
Angular dependence of interlayer magnetoresistance for antiferromagnetic Dirac semimetal $A$MnBi$_2$ ($A$=Sr, Eu) Peer-reviewed

M. Kondo, H. Sakai∗, M. Komada, H. Murakawa, and N. Hanasaki

JPS Conf. Proc.　30　011016　2020/03/19

DOI： 10.7566/JPSCP.30.011016 　
Bulk quantum Hall effect of spin-valley coupled Dirac fermions in the polar antiferromagnet BaMnSb2 Peer-reviewed

H. Sakai, H. Fujimura, S. Sakuragi, M. Ochi, R. Kurihara, A. Miyake, M. Tokunaga, T. Kojima, D. Hashizume, T. Muro, K. Kuroda, Takeshi Kondo, T. Kida, M. Hagiwara, K. Kuroki, M. Kondo, K. Tsuruda, H. Murakawa, N. Hanasaki

Physical Review B　101　(8)　081104(R)　2020/02/13
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.101.081104 　

ISSN： 2469-9950

eISSN： 2469-9969
Angle-dependent nontrivial phase in the Weyl semimetal NbAs with anisotropic Fermi surface Peer-reviewed

M. Komada, H. Murakawa, M. S. Bahramy, T. Kida, K. Yokoi, Y. Narumi, K. Kindo, M. Hagiwara, H. Sakai, and N. Hanasaki

Phys. Rev. B　101　(4)　045135-045135　2020/01/29
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevB.101.045135 　

ISSN： 2469-9950

eISSN： 2469-9969
新奇伝導現象を示すディラック・ワイル電子系強相関物質の開発 Invited

酒井英明

生産と技術　72　(1)　91-93　2020/01
圧力による電子バレー制御を利用した熱電性能の向上

酒井英明

クリーンエネルギー（日本工業出版）　28　(11)　20-24　2019/11
Giant enhancement of cryogenic thermopower by polar structural instability in the pressurized semimetal MoTe2 Peer-reviewed

Hidefumi Takahashi, Kento Hasegawa, Tomoki Akiba, Hideaki Sakai, Mohammad Saeed Bahramy, Shintaro Ishiwata

PHYSICAL REVIEW B　100　(19)　195130-195130　2019/11

DOI： 10.1103/PhysRevB.100.195130 　

ISSN： 2469-9950

eISSN： 2469-9969
High pressure synthesis of quasi-one-dimensional GdFeO3-type perovskite PrCuO3 with nearly divalent Cu ions Invited Peer-reviewed

M. Ito, H. Takahashi, H. Sakai, H. Sagayama, Y. Yamasaki, Y. Yokoyama, H. Setoyama, H. Wadati, K. Takahashi, Y. Kusano, S. Ishiwata

Chem. Commun.　55　(61)　8931-8934　2019/07

DOI： 10.1039/C9CC04656A 　

ISSN： 1359-7345

eISSN： 1364-548X
Defect-induced electronic structures on SnSe surfaces Peer-reviewed

K. Asakawa, F. Oguro, Y. Yoshida, H. Sakai, N. Hanasaki, Y. Hasegawa

Jpn. J. Appl. Phys.　58　SIIA06　2019/06

DOI： 10.7567/1347-4065/ab147d 　

ISSN： 0021-4922

eISSN： 1347-4065
Large Enhancement of Thermoelectric Efficiency Due to a Pressure-Induced Lifshitz Transition in SnSe Peer-reviewed

T. Nishimura, H. Sakai∗, H. Mori, K. Akiba, H. Usui, M. Ochi, K. Kuroki, A. Miyake, M. Tokunaga, Y. Uwatoko, K. Katayama, H. Murakawa, and N. Hanasaki

Phys. Rev. Lett.　122　(22)　226601　2019/06

DOI： 10.1103/PhysRevLett.122.226601 　

ISSN： 0031-9007

eISSN： 1079-7114
Nanoscale ice-type structural fluctuation in spinel titanetes Peer-reviewed

S. Torigoe, T. Hattori, K. Kodama, T. Honda, H. Sagayama, K. Ikeda, T. Otomo, H. Nitani, H. Abe, H. Murakawa, H. Sakai, N. Hanasaki

Phys. Rev. B　98　(13)　134443　2018/10
Publisher: American Physical Society (APS)
DOI： 10.1103/PhysRevB.98.134443 　

ISSN： 2469-9950

eISSN： 2469-9969
Negative-pressure-induced helimagnetism in ferromagnetic cubic perovskites Sr1-xBaxCoO3 Peer-reviewed

Hideaki Sakai

Physical Review Materials　2　104412　2018/10

DOI： 10.1103/PHYSREVMATERIALS.2.104412 　
Impact of antiferromagnetic order on Landau-level splitting of quasi-two-dimensional Dirac fermions in EuMnBi2 Peer-reviewed

Hideaki Sakai

Physical Review B　98　161108(R)　2018/10

DOI： 10.1103/PHYSREVB.98.161108 　
Quantitative evaluation of Dirac physics in PbTe Peer-reviewed

K. Akiba, A. Miyake, H. Sakai, K. Katayama, H. Murakawa, N. Hanasaki, S. Takaoka, Y. Nakanishi, M. Yoshizawa, M. Tokunaga

Phys. Rev. B　98　(11)　115144　2018/09

DOI： 10.1103/PhysRevB.98.115144 　

ISSN： 2469-9950

eISSN： 2469-9969
Evaluation of photo-induced shear strain in monoclinic VTe2 by ultrafast electron diffraction Peer-reviewed

A. Nakamura, T. Shimojima, M. Matsuura, Y. Chiashi, M. Kamitani, H. Sakai, S. Ishiwata, H. Li, A. Oshiyama, K. Ishizaka

Appl. Phys. Express　11　(9)　092601-092601　2018/08
Publisher: IOP Publishing
DOI： 10.7567/APEX.11.092601 　

ISSN： 1882-0778

eISSN： 1882-0786
Effect of uniaxial stress on the magnetic phases of CeAuSb2 Peer-reviewed

Hideaki Sakai

Physical Review B　98　024426　2018/07

DOI： 10.1103/PHYSREVB.98.024426 　
Electrochemical synthesis of phthalocyanine–molecular mixed crystals in dilute solution Peer-reviewed

R. Ishii, H. Murakawa, M. Nishi, M. Matsuda, H. Sakai, N. Hanasaki

Journal of Crystal Growth　487　92-95　2018/04/01
Publisher: Elsevier B.V.
DOI： 10.1016/j.jcrysgro.2018.02.023 　

ISSN： 0022-0248
Enhanced magnetoresistance in the binary semimetal NbAs2 due to improved crystal quality Peer-reviewed

K. Yokoi, H. Murakawa, M. Komada, T. Kida, M. Hagiwara, H. Sakai, N. Hanasaki

Phys. Rev. Materials　2　(2)　024203　2018/02

DOI： 10.1103/PhysRevMaterials.2.024203 　

ISSN： 2475-9953
Effect of applied orthorhombic lattice distortion on the antiferromagnetic phase of CeAuSb2 Peer-reviewed

Joonbum Park, Hideaki Sakai, Onur Erten, Andrew P. Mackenzie, Clifford W. Hicks

Physical Review B　97　(2)　024411　2018/01/11
Publisher: American Physical Society
DOI： 10.1103/PhysRevB.97.024411 　

ISSN： 2469-9969 2469-9950
Lattice Dynamics of 1T’-MoTe2 Studied by Time-Resolved Transmission X-Ray Diffraction at SACLA Peer-reviewed

T. Shimojima, A. Nakamura, K. Ishizaka, Y. Tanaka, K. Takubo, Y. Hirata, H. Wadati, S. Yamamoto, I. Matsuda, K. Ikeura, H. Takahashi, H. Sakai, S. Ishiwata, T. Togashi, S. Owada, T. Katayama, K. Tono, M. Yabashi, S. Shin

Adv. X-Ray. Chem. Anal., Japan　49　163-168　2018
High-Pressure Synthesis of Perovskite-Type Oxides with Unusually High Valence Iron/Cobalt Ions and Exploration of Novel Magnetic Phases Invited Peer-reviewed

ISHIWATA Shintaro, TAKAHASHI Hidefumi, SAKAI Hideaki

The Review of High Pressure Science and Technology　28　(3)　206-216　2018
Publisher: The Japan Society of High Pressure Science and Technology
DOI： 10.4131/jshpreview.28.206 　

ISSN： 0917-639X

More details Close

Recent progress on perovskite-type oxides with unusually high-valence Fe⁴⁺ and Co⁴⁺ ions, especially for the latter system, is reviewed with showing magnetic phase diagrams. All the compounds are obtained by high-pressure oxygen annealing for the oxygen-deficient perovskites in the form of polycrystalline or single-crystalline samples prepared at ambient pressure. While cubic perovskite-type SrFeO₃ has been found to show various types of novel helimagnetic phases, cubic perovskite-type SrCoO₃ known as a room-temperature ferromagnet has been revealed to show helimagnetic ordering either by Ba substitution or Ca substitution for Sr. These systems provide rich magnetic phase diagrams and anomalous cross-correlation effects such as a giant inverse magnetovolume effect, which are inherent to the strong p-d hybridization generating itinerant oxygen ligand holes.<br>
Magnetocaloric Materials with Multiple Instabilities Invited Peer-reviewed

Yasujiro Taguchi, Hideaki Sakai, Debraj Choudhury

ADVANCED MATERIALS　29　(25)　1606144　2017/07

DOI： 10.1002/adma.201606144 　

ISSN： 0935-9648

eISSN： 1521-4095
Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2 Peer-reviewed

M. Sakano, M. S. Bahramy, H. Tsuji, I. Araya, K. Ikeura, H. Sakai, S. Ishiwata, K. Yaji, K. Kuroda, A. Harasawa, S. Shin, K. Ishizaka

PHYSICAL REVIEW B　95　(12)　121101(R)　2017/03

DOI： 10.1103/PhysRevB.95.121101 　

ISSN： 2469-9950

eISSN： 2469-9969
Anticorrelation between polar lattice instability and superconductivity in the Weyl semimetal candidate MoTe2 Peer-reviewed

H. Takahashi, T. Akiba, K. Imura, T. Shiino, K. Deguchi, N. K. Sato, H. Sakai, M. S. Bahramy, S. Ishiwata

PHYSICAL REVIEW B　95　(10)　100501(R)　2017/03

DOI： 10.1103/PhysRevB.95.100501 　

ISSN： 2469-9950

eISSN： 2469-9969
磁石の中のスピン秩序を利用したディラック電子の制御 Invited Peer-reviewed

酒井英明

パリティ（丸善出版）　32　(1)　2017/01
Contrasting Magnetic Behaviors in Rhodium- and Ruthenium-Doped Cubic Perovskite SrFeO3: Nearly Ferromagnetic Metal versus Spin-Glass Insulator Peer-reviewed

Masataka Kinoshita, Hideaki Sakai, Naoaki Hayashi, Yoshinori Tokura, Mikio Takano, Shintaro Ishiwata

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION　55　(49)　15292-15296　2016/12

DOI： 10.1002/anie.201608222 　

ISSN： 1433-7851

eISSN： 1521-3773
Critical enhancement of thermopower in a chemically tuned polar semimetal MoTe2 Peer-reviewed

Hideaki Sakai, Koji Ikeura, Mohammad Saeed Bahramy, Naoki Ogawa, Daisuke Hashizume, Jun Fujioka, Yoshinori Tokura, Shintaro Ishiwata

SCIENCE ADVANCES　2　(11)　e1601378　2016/11

DOI： 10.1126/sciadv.1601378 　

ISSN： 2375-2548
ディラック電子の流れを制御できる新磁性体 Invited Peer-reviewed

酒井英明

パリティ（丸善出版）　31　(11)　2016/11
Relation between the structural phase transition and superconductivity in CuxIrTe2-ySey Peer-reviewed

M. Kamitani, H. Sakai, Y. Tokura, S. Ishiwata

PHYSICAL REVIEW B　94　(13)　134507　2016/10

DOI： 10.1103/PhysRevB.94.134507 　

ISSN： 2469-9950

eISSN： 2469-9969
新しい多層ディラック電子系EuMnBi2における磁気秩序と結合した量子伝導現象 Invited Peer-reviewed

酒井英明, 増田英俊, 石渡晋太郎

固体物理（アグネ）　51　(9)　2016/09
Field-temperature phase diagram and entropy landscape of CeAuSb2 Peer-reviewed

Lishan Zhao, Edward A. Yelland, Jan A. N. Bruin, Ilya Sheikin, Paul C. Canfield, Veronika Fritsch, Hideaki Sakai, Andrew P. Mackenzie, Clifford W. Hicks

PHYSICAL REVIEW B　93　(19)　195124　2016/05

DOI： 10.1103/PhysRevB.93.195124 　

ISSN： 2469-9950

eISSN： 2469-9969
Revealing the ultrafast light-to-matter energy conversion before heat diffusion in a layered Dirac semimetal Peer-reviewed

Y. Ishida, H. Masuda, H. Sakai, S. Ishiwata, S. Shin

PHYSICAL REVIEW B　93　(10)　100302　2016/03

DOI： 10.1103/PhysRevB.93.100302 　

ISSN： 2469-9950

eISSN： 2469-9969
Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions Peer-reviewed

Hidetoshi Masuda, Hideaki Sakai, Masashi Tokunaga, Yuichi Yamasaki, Atsushi Miyake, Junichi Shiogai, Shintaro Nakamura, Satoshi Awaji, Atsushi Tsukazaki, Hironori Nakao, Youichi Murakami, Taka-Hisa Arima, Yoshinori Tokura, Shintaro Ishiwata

Science Advances　2　(1)　e150111710.1126/sciadv.1501117　2016/01/01
Publisher: American Association for the Advancement of Science
DOI： 10.1126/sciadv.1501117 　

ISSN： 2375-2548
Rich structural phase diagram and thermoelectric properties of layered tellurides Mo1-xNbxTe2 Peer-reviewed

Koji Ikeura, Hideaki Sakai, Mohammad Saeed Bahramy, Shintaro Ishiwata

APL MATERIALS　3　(4)　041514　2015/04

DOI： 10.1063/1.4913967 　

ISSN： 2166-532X
Insulator-to-Superconductor Transition upon Electron Doping in a BiS2-Based Superconductor Sr1-xLaxFBiS2 Peer-reviewed

Hideaki Sakai, Daichi Kotajima, Kosuke Saito, Hiroki Wadati, Yuki Wakisaka, Masaichiro Mizumaki, Kiyofumi Nitta, Yoshinori Tokura, Shintaro Ishiwata

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　83　(1)　014709　2014/01

DOI： 10.7566/JPSJ.83.014709 　

ISSN： 0031-9015
Similarity of Scattering Rates in Metals Showing T-Linear Resistivity Peer-reviewed

J. A. N. Bruin, H. Sakai, R. S. Perry, A. P. Mackenzie

SCIENCE　339　(6121)　804-807　2013/02

DOI： 10.1126/science.1227612 　

ISSN： 0036-8075

eISSN： 1095-9203
Soft phonon mode coupled with antiferromagnetic order in incipient-ferroelectric Mott insulators Sr1-xBaxMnO3 Peer-reviewed

H. Sakai, J. Fujioka, T. Fukuda, M. S. Bahramy, D. Okuyama, R. Arita, T. Arima, A. Q. R. Baron, Y. Taguchi, Y. Tokura

PHYSICAL REVIEW B　86　(10)　104407　2012/09

DOI： 10.1103/PhysRevB.86.104407 　

ISSN： 1098-0121
Thermoelectric Properties of Electron-Doped SrMnO3 Single Crystals with Perovskite Structure Peer-reviewed

T. Suzuki, H. Sakai, Y. Taguchi, Y. Tokura

JOURNAL OF ELECTRONIC MATERIALS　41　(6)　1559-1563　2012/06

DOI： 10.1007/s11664-011-1860-1 　

ISSN： 0361-5235
Emergent phenomena in perovskite-type manganites Peer-reviewed

Y. Taguchi, H. Sakai, D. Okuyama, S. Ishiwata, J. Fujioka, T. Fukuda, D. Hashizume, F. Kagawa, Y. Takahashi, R. Shimano, Y. Tokunaga, Y. Kaneko, A. Nakao, H. Nakao, Y. Murakami, K. Sugimoto, M. Takata, K. Yamauchi, S. Picozzi, A. Q. R. Baron, T. Arima, Y. Tokura

PHYSICA B-CONDENSED MATTER　407　(11)　1685-1688　2012/06

DOI： 10.1016/j.physb.2012.01.006 　

ISSN： 0921-4526
Displacement-Type Ferroelectricity with Off-Center Magnetic Ions in Perovskite Sr1-xBaxMnO3 Peer-reviewed

H. Sakai, J. Fujioka, T. Fukuda, D. Okuyama, D. Hashizume, F. Kagawa, H. Nakao, Y. Murakami, T. Arima, A. Q. R. Baron, Y. Taguchi, Y. Tokura

PHYSICAL REVIEW LETTERS　107　(13)　137601　2011/09

DOI： 10.1103/PhysRevLett.107.137601 　

ISSN： 0031-9007

eISSN： 1079-7114
Magnetically driven ferroelectric atomic displacements in orthorhombic YMnO3 Peer-reviewed

D. Okuyama, S. Ishiwata, Y. Takahashi, K. Yamauchi, S. Picozzi, K. Sugimoto, H. Sakai, M. Takata, R. Shimano, Y. Taguchi, T. Arima, Y. Tokura

PHYSICAL REVIEW B　84　(5)　054440　2011/08

DOI： 10.1103/PhysRevB.84.054440 　

ISSN： 1098-0121
Electron doping in the cubic perovskite SrMnO3: Isotropic metal versus chainlike ordering of Jahn-Teller polarons Peer-reviewed

H. Sakai, S. Ishiwata, D. Okuyama, A. Nakao, H. Nakao, Y. Murakami, Y. Taguchi, Y. Tokura

PHYSICAL REVIEW B　82　(18)　180409(R)　2010/11

DOI： 10.1103/PhysRevB.82.180409 　

ISSN： 1098-0121
Impact of Bicritical Fluctuation on Magnetocaloric Phenomena in Perovskite Manganites Peer-reviewed

Hideaki Sakai, Yasujiro Taguchi, Yoshinori Tokura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　78　(11)　113708　2009/11

DOI： 10.1143/JPSJ.78.113708 　

ISSN： 0031-9015
Composite domain walls in a multiferroic perovskite ferrite Peer-reviewed

Yusuke Tokunaga, Nobuo Furukawa, Hideaki Sakai, Yasujiro Taguchi, Taka-hisa Arima, Yoshinori Tokura

NATURE MATERIALS　8　(7)　558-562　2009/07

DOI： 10.1038/NMAT2469 　

ISSN： 1476-1122

eISSN： 1476-4660
Dopant-Dependent Impact of Mn-Site Doping on Critical-State Manganites R0.6Sr0.4MnO3 (R = La, Nd, Sm, and Gd) Peer-reviewed

Hideaki Sakai, Kiminori Ito, Takayuki Nishiyama, Xiuzhen Yu, Yoshio Matsui, Shigeki Miyasaka, Yoshinori Tokura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　77　(12)　124712　2008/12

DOI： 10.1143/JPSJ.77.124712 　

ISSN： 0031-9015
Current-induced persistent magnetization in a relaxorlike manganite Peer-reviewed

H. Sakai, Y. Tokura

APPLIED PHYSICS LETTERS　92　(10)　102514　2008/03

DOI： 10.1063/1.2897299 　

ISSN： 0003-6951
Fe-doping-induced evolution of charge-orbital ordering in a bicritical-state manganite Peer-reviewed

H. Sakai, K. Ito, R. Kumai, Y. Tokura

PHYSICAL REVIEW B　76　(15)　155112　2007/10

DOI： 10.1103/PhysRevB.76.155112 　

ISSN： 1098-0121
Reversible resistive switching in Bi4Ti3O12 thin films deposited by electron cyclotron resonance sputtering Peer-reviewed

Yoshito Jin, Hideaki Sakai, Masaru Shimada

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS　45　(4B)　3243-3246　2006/04

DOI： 10.1143/JJAP.45.3243 　

ISSN： 0021-4922
Effective-mass approach to interaction effects on electronic structure in carbon nanotubes Peer-reviewed

H Sakai, H Suzuura, T Ando

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES　22　(1-3)　704-707　2004/04

DOI： 10.1016/j.physe.2003.12.104 　

ISSN： 1386-9477
Effective-mass theory of electron correlations in band structure of semiconducting carbon nanotubes Peer-reviewed

H Sakai, H Suzuura, T Ando

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN　72　(7)　1698-1705　2003/07

DOI： 10.1143/JPSJ.72.1698 　

ISSN： 0031-9015

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Presentations 25

Dirac fermions in complex magnets with Bi square nets International-presentation Invited

H. Sakai

The 24th Taiwan-Japan-Korea Symposium on Strongly Correlated Electron Systems (TJK24)　2026/03/05
A homologous series of layered magnetic topological semimetals International-presentation

H. Sakai, A. Yamashita, R. Mizuno, M. Ochi, et al

Pacifichem 2025　2025/12/19
High-field transport & lattice instability in SrCdBi2 with a 2D Bi layer International-presentation

H. Sakai

1000-Tesla Science Workshop　2025/12/07
Interplay of Dirac fermions and complex magnetic order in inorganic materials Invited

2025/09/16
ThCr2Si2型Ce磁性層を有するBi正方格子物質Ce3Au4Ge2Bi4における特異なディラック電子状態

酒井英明, 山下淳志, 水野竜太, 越智正之, 他

日本物理学会 2025年春季大会　2025/03/21
P T 対称な反強磁性体の非相反伝導現象 Invited

酒井英明

学術変革領域 (A) トピカルミーティング「精密計測 × アシンメトリ量子物質」　2025/02/09
Current-induced Nematic Dirac Valleys in SrMnBi2 with Odd-parity Multipole Invited

H. Sakai

UMMS24 (Max-Planck Institute CPfS seminar)　2024/09/04
Control of lattice and magnetism of layered Dirac materials: Material design and uniaxial stress Invited

H. Sakai

Elast-Q-Mat Colloquia　2024/05/02
Exploration of Dirac/Weyl magnets based on the block-layer concept Invited

H. Sakai

Max-Planck Institute CPfS seminar　2023/08/23
特異なスピン分裂バンドを有するトポロジカル磁性体の輸送現象 Invited

酒井英明

第2回「第一原理計算と機械学習の進歩と調和」研究会　2023/06/05
ブロック層制御による磁性・極性トポロジカル物質の開拓 Invited

酒井英明

金研研究会ー強相関物質における創発物性研究の現状と将来展望　2023/04/22
Block-layer Design of Magnetic and Polar Dirac/Weyl Semimetals International-presentation Invited

H. Sakai

The 6th Symposium for the Core Research Clusters for Materials Science and Spintronics, and the 5th Symposium on International Joint Graduate Program in Materials Science　2022/10/25
Tunable spin-valley coupling and nonreciprocal transport in polar Dirac metal BaMn$X_2$ ($X$=Sb, Bi) International-presentation

H. Sakai, M. Kondo, M. Ochi, T. Kojima, R. Kurihara, M. Kimata, K. Sudo, D. Sekine, M. Matsubara, A. Miyake, M. Tokunaga, K. Kuroki, H. Murakawa, N. Hanasaki

29th International Conference on Low Temperature Physics (LT29)　2022/08/20
磁性・極性を有するディラック・ワイル半金属の強磁場輸送現象 Invited

酒井英明

ISSPワークショップ--1000テスラ超強磁場科学の開拓　2022/06/11
Block-layer design for high-mobility magnetic and polar Dirac materials International-presentation Invited

H. Sakai

SMS2022 (Summit of Materials Science 2022)　2022/03/02
Tuning Thermoelectric Performance for a Layered Dirac Material with High-mobility Carriers International-presentation Invited

H. Sakai

MRM2021 (Materials Research Meeting)　2021/12/15
Spin/valley-polarized quantum transport in magnetic and polar Dirac materials International-presentation Invited

H. Sakai

Asia-Pacific Conference on Condensed Matter Physics 2021 (AC2MP2021)　2021/12/01
量子物質研究と強磁場 –最近の潮流と展望 Invited

酒井英明

強磁場コラボラトリ 2030 シンポジウム　2020/12/03
Quantum transport coupled with magnetic order and lattice polarization in layered Dirac materials International-presentation Invited

H. Sakai

ARHMF2020 (Asian regional high-field conference)　2020/12/02
Dirac fermions couples with magnetic order and lattice polarization International-presentation Invited

H. Sakai

APCTP-KPS-JPS joint meeting on “New trends in quantum and topological matters under extreme condition”　2020/11/06
磁性・極性と結合した量子伝導を示すトポロジカル層状物質の開拓 Invited

酒井英明

ISSP ワークショップ–量子物質研究の最近の進展と今後の展望　2020/09/24
第一回強磁場フォーラムフロンティア奨励賞講演「強磁場を用いたディラック電子系磁性体の強相関量子輸送現象の解明」 Invited

酒井英明

物性研短期研究会/強磁場科学研究会–強磁場コラボラトリーによる強磁場科学の新展開　2019/12/04
Bulk Half-integer Quantum Hall Effect in Dirac Antiferromagnet BaMnSb2 International-presentation

H. Sakai, H. Fujimura, R. Kurihara, A. Miyake, M. Tokunaga, T. Kida, M. Hagiwara, K. Tsuruda, H. Murakawa, N. Hanasaki

The International Conference on Strongly Correlated Electron Systems 2019 (SCES2019)　2019/09/28
Correlated quantum transport in layered Dirac antiferromagnets International-presentation Invited

H. Sakai

Cond Mat Seminars (School of Physics and Astronomy, University of St Andrews)　2019/05/19
Bulk quantum Hall effect of massless Dirac fermions in BaMnSb2 International-presentation Invited

H. Sakai

Workshop on Spin-Orbit Interaction and G-factor (SOIG2019)　2019/05/09

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Industrial Property Rights 7

記録再生装置

酒井英明, 神好人, 嶋田勝, 榎本陽一

特許第4071786号

Property Type: Patent
ターゲット

神好人, 酒井英明, 嶋田勝, 木内幹保

特許第4441646号

Property Type: Patent
メモリ装置

酒井英明, 神好人, 嶋田勝, 榎本陽一

特許第4490323号

Property Type: Patent
2安定抵抗値取得装置及びその製造方法

神好人, 酒井英明, 嶋田勝

特許第4559425号

Property Type: Patent
白金薄膜の形成法

赤澤方省, 酒井英明, 神好人, 嶋田勝

特許第 4680752 号

Property Type: Patent
2安定抵抗値取得装置及びその製造方法

神好人, 酒井英明, 嶋田勝

特許第5189613号

Property Type: Patent
マンガン酸化物、マンガン酸化物を備える強誘電体メモリ素子、および強誘電体メモリ装置

酒井英明, 田口康二郎, 十倉好紀

特許第5846571号

Property Type: Patent

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Research Projects 13

奇パリティ多極子磁性体の振動発電

酒井英明

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 挑戦的研究(萌芽)

Institution: 大阪大学

2025/06/27 - 2028/03/31
Exploration and elucidation of band electrons at 1000 T

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Transformative Research Areas (A)

Institution: The University of Tokyo

2023/04/01 - 2028/03/31
p電子系の特異なg因子を活かした高度スピン変換機能の開拓

伏屋雄紀, 白石誠司, 平原徹, 酒井英明

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(A)

Institution: 電気通信大学

2023/04 - 2027/03

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本研究では，目的を達成するために（１）Biと（２）ポストBi物質（IV-VI族半導体と層状ディラック物質）の２系統を平行して研究を進めている． (1-1) Biにおいてg因子の異方性を考慮したスピンホール効果の計算を行った．g因子およびその異方性を，独自に開発したπ-matrix法を用いて計算した結果，Biのスピン変換効率を定量的に求めることが出来た．スピン流の定義の違いによるスピンホール伝導度計算の違いを明らかにし，スピン磁気モーメントの流れに基づく定義が実験結果と矛盾しないことを明らかにした． (1-2) キャリア密度変化に由来する弾性抵抗の理論の基本的枠組みを構築した．あわせて，Biにおいて弾性抵抗の測定を行った．その結果，応力によりバレー自由度が制御できることを明らかにした．さらに，第一原理計算に基づいてバンド構造の一軸応力による変化を計算し，実験で得られた弾性抵抗の変化がキャリア密度の変化で説明できることを明らかにした． (2-1) 二次元ビスマス層を有する物質系の基本物質であるEuMnBi2において，g因子のフェルミエネルギー依存性を量子振動測定により解明した．フェルミエネルギーがディラックバンドの電荷中性点に近づくと，g因子が増大することを明らかにした．得られた成果を論文として発表した． (2-2) in situ ホール効果測定システムを立ち上げ，磁性トポロジカル絶縁体ヘテロ構造MnBi2Te4/Bi2Te3の磁化特性の評価を行った．基板とBi2Te3の界面におけるBi原子１層の有無により，観測される異常ホール効果が異なり，Biのスピン軌道結合由来の異常ホール効果が起きることが分かった．
スピン・バレー結合した超高易動度ディラック電子の新奇非相反・非線形伝導現象の開拓

酒井英明, 木俣基

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(A)

Institution: 大阪大学

2022/04/01 - 2026/03/31

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本研究では、極性・磁性を持つディラック・ワイル半金属を対象に、元素置換や外部応力により、ディラック・ワイル電子状態のスピン・バレー結合、スピン分裂、ベリー位相、キャリア濃度を系統的に制御することで、非相反・非線形伝導の微視的メカニズムを解明し、その効果の巨大化を目指す。2023年度は、極性ディラック半金属BaMnX2を対象に、基本物質X =Sbよりも複雑な二種類のバレーからなる X =Bi において非相反伝導の測定を行った。X =Sb の場合と同様に FIB加工により，単一ドメイン内において電流方向の異なる二種類のデバイスを作製し、それぞれの非相反伝導特性を比較した。その結果、両者の非相反抵抗率には顕著な温度依存性の違いがあることを見出した。X=Sbでは、非相反抵抗率は室温から低温に向かって単調に増加するのに対し、X=Biでは低温でピークを示す非単調な挙動が確認された。このような顕著な違いは，X =Sb と X =Bi のスピン・バレー状態の違いに起因することを、バンド計算に基づき定性的に説明することに成功し、これらの成果は学術論文として発表された。さらに、外部応力により格子歪みを変化させ，非相反効果を制御することを目指した。これに向け，独マックスプランク研究所(ドレスデン)に出張し，同研究所で開発された一軸性圧力印加セルを用いた実験を実施した。この実験では、常圧下で正方格子を有する本物質系の単結晶に対し、数十MPa程度の微弱な一軸応力を印加することで、明瞭な格子のソフト化を観測した。これにより、本物質系の結晶構造が外部応力に対して非常に敏感であることが明らかとなった。
Developing novel topological superconductors

Sakai Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Osaka University

2022/06/30 - 2025/03/31

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We studied iron-based superconductors with a putative topological insulating layer embedded, aiming to explore a new class of materials suitable for Majorana fermions. We successfully grew single crystals of approximately 1 mm in size and established a synthesis method that enables control of electron doping. From the magnetization measurements on the obtained crystals, we determined the superconducting transition temperature (Tc) via the Meissner effect. We found that Tc varies significantly depending on the A-site element.
Study of quantum transport phenomena in Dirac magnets with spontaneous magnetisation

Sakai Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Osaka University

2019/04 - 2022/03

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In this study, we have explored novel (weak) ferromagnetic layered Dirac materials, where quantum transport phenomena can be controlled by spontaneous magnetization. In BaMnX2, which exhibits weak ferromagnetism due to the canted Mn spins, we found that the X square lattice is slightly distorted and in-plane polarity is generated. This distortion induces not only spontaneous magnetization but also spin-valley locking of the Dirac electrons via the spin-orbit interactions. This peculiar electronic state results in unconventional magnetotransport phenomena at weak magnetic fields. In the antiferromagnet EuMnBi2 exhibiting strong coupling to magnetism, we have demonstrated that the spontaneous magnetization and Fermi energy can be systematically controlled by partially substituting Eu ions with other rare earth ions.
Exploring novel magnets hosting a honeycomb network and their anomalous magneto-electric effect

Sakai Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Osaka University

2019/06 - 2021/03

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In this research project, we aimed at exploring new magnets hosting a honeycomb lattice, since some theoretical studies predicted novel magneto-electric effects due to the non-collinear spin order. To achieve this, we adopted an antiferromagnet hosting a buckled honeycomb structure, which is useful to vary the magnetic order by applying uniaxial strain. Consequently, we have found that the AM2X2 materials host electronic structures sensitive to the external strain. Furthermore, we explored ferromagnet hosting a honeycomb structure. We focused on CrGeTe3, where we succeeded in increasing the ferromagnetic transition temperature by doping hole carriers.
Enhancement of thermoelectric efficiency by combining organic and inorganic materials

Hanasaki Noriaki, Sakai Hideaki, Murakawa Hiroshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Osaka University

2016/04 - 2019/03

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In the thermoelectric materials, the acoustic phonon, which contributes to the heat conductance, is scattered by the rattling of the atoms. The organic molecules have many intramolecular vibration modes. These many modes have the advantage of the scattering of the phonon. We studied the effect of the intercalation of the organic cations such as hexylamine into the inorganic layered compound SnSe2 by the electrochemical methods. The electric conductivity increases by the electron doping, and the heat conductivity decreases, since the organic molecules cause the scattering of the phonon. By the intercalation of the organic molecules, we succeeded in the enhancement of the dimensionless figure of merit.
Study of magnets hosting strongly correlated Dirac fermions

Sakai Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Young Scientists (A)

Institution: Osaka University

2016/04 - 2019/03

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In this research, we aimed to study the correlated quantum transport phenomena in a layered bulk magnet EuMnBi2 to reveal the fundamental physics of Dirac fermions coupled with magnetism. To show the variation of band structure upon the antiferromagnetism in EuMnBi2, we have first studied the Landau level splitting in a tilted magnetic field up to ~35 T and found effective g factor differs by ~50% between two antiferromagnetic phases, which reflects the strong exchange coupling with Eu spins as verified by first-principles calculations. We have also studied the details of field-tunable antiferromagnetic order of both Eu and Mn layers by the neutron diffraction and discussed its impact on the spin-flop-induced giant magnetoresistance effects in the present system.
Exploration of novel materials hosting post-graphene atomic layers by high-pressure synthesis and electrochemical intercalation

Sakai Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Osaka University

2015/04 - 2017/03

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To explore the post-graphene materials, we have synthesised several new materials hosting functional conducting layers, such as honeycomb and square nets, by utilising a high-pressure synthesis method. We have succeeded in carrier doping in black phosphorus that consists of the stacking of phosphorus honeycomb sheets (phosphorene), by substituting phosphorus with germanium and silicon. We have also synthesised a transition metal dichalcogenide with the polar layer stacking and a new layered magnet hosting quasi 2D Dirac fermions on the bismuth square net. Furthermore, aiming at wide-range carrier doping in the newly-developed post-graphene materials, we have performed electrochemical intercalation of organic molecules. We focused on a transition metal dichalcogenide as a first target, and have successfully optimised its thermoelectric figure of merit by enhancing thermoelectric power factor and reducing the thermal conductivity.
Search for high-mobility thermoelectric material with super-ionic conductivity and control of lattice disorder

ISHIWATA Shintaro, SAKAI Hiswaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: The University of Tokyo

2013/04 - 2015/03

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To search for a high-performance thermoelectric material showing low thermal conductivity as low as a glass in addition to high electronic conductivity, we studied the effect of controlling domain on thermoelectric properties and synthesized new compounds of layered transition-metal chalcogenides. First, we found that a polycrystalline sample of CuAgSe with superionic conductivity shows an enhanced power factor at low temperatures below 200 K by enlarging the size of domains. Second, we examined Nb-doping effect on 1T-MoTe2, which is known as a high-mobility semimetal, and found that the 10%-doped sample shows an improved figure of merit (ZT~0.02) at room temperature and that the 60%-doped sample crystallizes in new 3R polytype without inversion symmetry.
Study of electron-doped manganite single crystals using high-pressure synthesis methods

SAKAI Hideaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Young Scientists (B)

Institution: The Institute of Physical and Chemical Research

2010 - 2011

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So far, there have been few studies on "electron-doped" manganites, the Mn valence of which is close to 4+. By using high-pressure synthesis methods, recently, we succeeded in synthesizing the single crystals of SrMnO_3, which is a parent compound with Mn^<4+> ions. In this project, by controlling the carrier number and/or lattice constant with partial substitution of Sr ions, we have revealed the overall features of electronic and lattice states for the electron-doped manganites. In particular, we have found a novel insulator-metal transition accompanied by a magnetic transition, which is controllable with 1% carrier doping. Furthermore, we have discovered a ferroelectric transition with off-center Mn^<4+> ions by substituting Sr ions with Ba ions. The ferroelectric properties are much nicer than those for the conventional multiferroic materials. These materials would be quite promising for future spintronic technology.
強相関リラクサー物質の開拓とその相制御

酒井英明

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 特別研究員奨励費

Institution: 東京大学

2007 - 2008

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ペロブスカイト型マンガン酸化物では、強磁性金属相と電荷軌道整列絶縁体相の異なる二相が競合している。相境界(臨界点)近傍の物質では、磁場印加や不純物ドープに対して、二相の転換が生じるため巨大応答が現れる。例えば、不純物効果に関して、電荷軌道整列相が数%のCrドープにより融解し、強磁性金属相が誘起されることが知られている。これとは反対に、近年我々は強磁性金属相における不純物効果を調べ、Feドープが強磁性金属を弱体化させ電荷軌道整列を誘起することを見出した。このような効果は、臨界点付近の物質のみで確認されており、本年度の研究ではさらにその普遍性を解明するため、R0.6Sr0.4Mn03なる強磁性金城(R=La,Nd,Sm)-短距離電荷軌道整列スピングラス絶縁体(R=Gd)の臨界系にてFeドープ効果を調べた。本系はRを変化させバンド幅を減少させることにより、強磁性転移温度を375Kから120Kまで幅広く変えられるため、Feドープ効果の変化を系統的に調べることができる。強磁性金属を示すR=La-Smでは、Feドープにより強磁性転移温度は急激に減少し、スピングラス絶縁体相が現れる。透過型電子顕微鏡やラマン散乱測定により、これらのスピングラス相では電荷軌道整列相関が発達していることが明らかとなった。さらに、R=Gdにおける不純物効果についても詳細に調べた。Feドープでは顕著な効果が現れないが、Crドープでは短距離電荷軌道整列状態が破壊され強磁性金属が誘起されることが観測された。以上より、FeとCrの対照的なドープ効果は、系のバンド幅やホール濃度、秩序相の相関長などによらず普遍的に成立することがわかった。本成果は、マンガン酸化物の相競合状態を、不純物の種類を変化させることにより双方向に制御できることか示唆しており、磁場かどか用いかい新たな臨界状態相制御法を確立する結果となった。

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