Updated on 2024/03/21

写真a

 
HIRAI Daigorou
 
Organization
Graduate School of Engineering Applied Physics 2 Associate professor
Graduate School
Graduate School of Engineering
Undergraduate School
School of Engineering Physical Science and Engineering
Title
Associate professor

Degree 1

  1. Doctor (Science) ( 2011.3   The University of Tokyo ) 

Research Interests 1

  1. Solid state chemistry, Condensed matter physics

Research Areas 3

  1. Nanotechnology/Materials / Inorganic materials and properties

  2. Natural Science / Magnetism, superconductivity and strongly correlated systems

  3. Natural Science / Magnetism, superconductivity and strongly correlated systems

Current Research Project and SDGs 2

  1. Exploration of materials and functionality in transition metal compounds derived from spin-orbit interaction

  2. Development of stable and safe oxide topological materials

Research History 8

  1. Nagoya University   Graduate School of Engineering Applied Physics 2   Associate professor

    2022.5

  2. Nagoya University   Graduate School of Engineering Applied Physics   Associate professor

    2022.5

  3. The University of Tokyo   Materials Design and Characterization Laboratory Affiliated to the ISSP   Reserch associate

    2015.2 - 2022.4

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    Country:Japan

  4. The University of Tokyo   Institute for Solid State Physics   Assistant Professor

    2015.2 - 2022.4

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    Country:Japan

  5. The University of Tokyo   Graduate School of Science   Postdoctoral Fellow

    2013.3 - 2015.1

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    Country:Japan

  6. The University of Tokyo   Department of Physics   Researcher   Project Researcher

    2013.3 - 2015.1

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    Country:Japan

  7. Princeton University   Department of Chemistry   Postdoctoral Fellow

    2011.5 - 2013.2

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    Country:United States

  8. Princeton University   Department of Chemistry   Researcher   Postdoctoral Research Associate

    2011.5 - 2013.2

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    Country:United States

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Education 2

  1. The University of Tokyo   Department of Advanced Materials Science

    2006.4 - 2011.3

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    Country: Japan

  2. The University of Tokyo   Department of Enginnering   Applied Chemistry

    2002.4 - 2006.4

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    Country: Japan

Professional Memberships 1

  1. Physical Society of Japan

    2005.8

Committee Memberships 1

  1. 日本物理学会   領域8(強相関電子系分野)運営委員長  

    2020.4 - 2021.3   

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    Committee type:Academic society

Awards 4

  1. Yazaki Academic Incentive Award

    2023.6   Japan Association for Chemical Innovation  

    Daigorou Hirai

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    Award type:Award from publisher, newspaper, foundation, etc.  Country:Japan

  2. Yazaki Academic Incentive Award

    2022.1   Yazaki Memorial Foundation for Science and Technology  

    Daigorou Hirai

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    Award type:Award from publisher, newspaper, foundation, etc.  Country:Japan

  3. ISSP Young Scientist Medal

    2020.3   The Institute for Solid State Physics, The University of Tokyo  

    Daigorou Hirai

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    Country:Japan

  4. Young Scientist Award of the Physical Society of Japan

    2020.3   The Physical Society of Japan  

    Daigorou Hirai

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    Award type:Award from Japanese society, conference, symposium, etc.  Country:Japan

 

Papers 92

  1. Electroactive actuator composites using volume change induced by insulator-to-metal transition in VO2 Reviewed

    K. Takenaka, Y. Mizuno, J. Shibutani, K. Kishida, K. Takada, K. Yagi, Y. Yokoyama, N. Katayama, Y. Okamoto, D. Hirai, T. Hatano, A. Fujita

    Applied Physics Letters   Vol. 123 ( 23 )   2023.12

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

    This report describes the actuator functionality of a ceramic composite that uses the volume change caused by the insulator–metal (I–M) transition of VO2. When an electrical field was applied at 295 K, 50 vol. %-VO2/Al2O3 ceramic composite underwent the I–M transition because the VO2 powder dispersed in the composite became metallic. Simultaneous measurement of I–V characteristics and linear strain demonstrated that this I–M transition was accompanied by a positive strain. This strain increased with increase in the limit current value, which limits excessive current flow after transition. The strain exceeded 1300 ppm at maximum. Its magnitude corresponded to the volume change obtained from thermal expansion measurements on the composite. This composite performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials.

    DOI: 10.1063/5.0175670

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  2. Superconductivity induced by doping holes in the nodal-line semimetal NaAlGe Reviewed

    Toshiya Ikenobe, Takahiro Yamada, Daigorou Hirai, Hisanori Yamane, Zenji Hiroi

    Physical Review Materials   Vol. 7 ( 10 )   2023.10

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

    DOI: 10.1103/PhysRevMaterials.7.104801

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.7.104801/fulltext

  3. Fermi surface and light quasi particles in hourglass nodal chain metal ß-ReO<sub>2</sub> Reviewed

    Hirai, D; Anbai, T; Konoike, T; Uji, S; Hattori, Y; Terashima, T; Ishikawa, H; Kindo, K; Katayama, N; Oguchi, T; Hiroi, Z

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 35 ( 40 )   2023.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Physics Condensed Matter  

    Quantum oscillations (QOs) in magnetic torque and electrical resistivity were measured to investigate the electronic structure of β-ReO2, a candidate hourglass nodal chain (NC) metal (Dirac loop chain metal). All the de Haas-van Alphen oscillation branches measured at 30 mK in magnetic fields of up to 17.5 T were consistent with first-principles calculations predicting four Fermi surfaces (FSs). The small-electron FS of the four FSs exhibited a very small cyclotron mass, 0.059 times that of the free electrons, which is likely related to the linear dispersion of the energy band. The consistency between the QO results and band calculations indicates the presence of the hourglass NC predicted for β-ReO2 in the vicinity of the Fermi energy.

    DOI: 10.1088/1361-648X/ace22c

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  4. Superconductivity in Ternary Scandium Telluride Sc<sub>6</sub><i>M</i>Te<sub>2</sub> with 3<i>d</i>, 4<i>d</i>, and 5<i>d</i> Transition Metals Reviewed

    Yusaku Shinoda, Yoshihiko Okamoto, Youichi Yamakawa, Haruka Matsumoto, Daigorou Hirai, Koshi Takenaka

    Journal of the Physical Society of Japan   Vol. 92 ( 10 )   2023.8

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

    DOI: 10.7566/JPSJ.92.103701

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  5. Superconductivity in High-Entropy Antimonide M<sub>1-<i>x</i> </sub>Pt<sub> <i>x</i> </sub>Sb (M = Equimolar Ru, Rh, Pd, and Ir) Reviewed

    Hirai, D; Uematsu, N; Saitoh, K; Katayama, N; Takenaka, K

    INORGANIC CHEMISTRY   Vol. 62 ( 35 ) page: 14207 - 14215   2023.8

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

    The high-entropy concept was applied to the synthesis of transition-metal antimonides, M1-xPtxSb (M = equimolar Ru, Rh, Pd, and Ir). High-entropy antimonide samples crystallized in a pseudo-hexagonal NiAs-type crystal structure with a P63/mmc space group were successfully synthesized through a conventional solid-state reaction and subsequent quenching. A detailed investigation of the composition and equilibration conditions confirmed the reversible phase transition between a multiphase state at low temperature and an entropy-driven single-phase solid solution at high temperatures. Electrical resistivity, magnetization, and heat capacity measurements of single-phase M1-xPtxSb (x = 0.2) samples revealed a bulk superconducting transition at 2.15(2) K. This study demonstrates that the high-entropy concept provides numerous opportunities for the discovery of new functional materials such as superconductors.

    DOI: 10.1021/acs.inorgchem.3c01364

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  6. Development of Negative Thermal Expansion Material Utilizing Structural Phase Transition of Zn<sub>2</sub>P<sub>2</sub>O<sub>7</sub>

    KASUGAI Ryota, KADOWAKI Yoshifumi, KATAYAMA Naoyuki, HIRAI Daigorou, TAKENAKA Koshi

    Journal of the Japan Society of Powder and Powder Metallurgy   Vol. 70 ( 8 ) page: 371 - 375   2023.8

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Japan Society of Powder and Powder Metallurgy  

    <p>Large negative thermal expansion (NTE) was achieved at room temperature using the structural phase transition in Zn<sub>2</sub>P<sub>2</sub>O<sub>7</sub>. Particularly, Zn<sub>1.6</sub>Mg<sub>0.4</sub>P<sub>2</sub>O<sub>7</sub> has a negative coefficient of linear thermal expansion <i>αL</i> of about –60 ppm/K at temperatures of 289–374 K. Co-doping of Mg and another element at the Zn site was found to be effective for control of NTE properties and for improvement of thermal expansion compensating ability. The present phosphates are expected to have widely various practical applications as thermal expansion compensators because they contain no toxic or expensive elements. Moreover, they can be prepared using a simple solid-state reaction method in air.</p>

    DOI: 10.2497/jjspm.23-00009

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    CiNii Research

  7. Anomalous Diamagnetic Torque Signals in Topological Nodal-Line Semimetal NaAlSi Reviewed

    Shinya Uji, Takako Konoike, Yuya Hattori, Taichi Terashima, Tamio Oguchi, Takahiro Yamada, Daigorou Hirai, Toshiya Ikenobe, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 92 ( 7 )   2023.7

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

    DOI: 10.7566/JPSJ.92.074703

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  8. Successive phase transitions of the spin-orbit-coupled metal Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> probed by high-resolution synchrotron x-ray diffraction Reviewed

    Hirai, D; Fukui, A; Sagayama, H; Hasegawa, T; Hiroi, Z

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 35 ( 3 )   2023.1

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Physics Condensed Matter  

    The 5d pyrochlore oxide superconductor Cd2Re2O7 (CRO) has attracted significant interest as a spin-orbit-coupled metal (SOCM) that spontaneously undergoes a phase transition to an odd-parity multipole phase by breaking the spatial inversion symmetry due to the Fermi liquid instability caused by strong spin-orbit coupling. Despite the significance of structural information during the transition, previous experimental results regarding lattice deformation have been elusive. We have conducted ultra-high resolution synchrotron radiation x-ray diffraction experiments on a high-quality CRO single crystal. The temperature-dependent splitting of the 0 0 16 and 0 0 14 reflections, which are allowed and forbidden, respectively, in the high-temperature cubic phase I (space group Fd-3m), has been clearly observed and reveals the following significant facts: inversion symmetry breaking and tetragonal distortion occur simultaneously at T s1 = 201.5(1) K; the previously believed first-order transition between phase II (I-4m2) and phase III (I4122) at T s2 ∼120 K consists of two close second-order transitions at T s2 = 115.4(1) K and T s3 ∼ 100 K; there is a new orthorhombic phase XI (F222) in between. The order parameters (OPs) of these continuous transitions are uniquely represented by a two-dimensional irreducible representation Eu of the Oh point group, and the OPs of phase XI are a linear combination of those of phases II and III. Each phase is believed to correspond to a distinct odd-parity multipole order, and the complex successive transitions observed may be the result of an electronic phase transition that resolves the Fermi liquid instability in the SOCM.

    DOI: 10.1088/1361-648X/aca05e

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  9. Large magnetic-field-induced strains in sintered chromium tellurides Reviewed International journal

    Yuki Kubota, Yoshihiko Okamoto, Tomoya Kanematsu, Takeshi Yajima, Daigorou Hirai, Koshi Takenaka

    APPLIED PHYSICS LETTERS   Vol. 122 ( 4 )   2023.1

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    Sintered samples of Cr3Te4 and Cr2Te3 are found to show large strains accompanied by large volume changes under a magnetic field. In Cr3Te4, volume increases of delta V/V = 500-1170 ppm by applying a magnetic field of 9 T are observed over the entire temperature range below 350 K. At room temperature, the delta V/V value exceeds 1000 ppm, which is considerably larger than the maximum values reported for Cr-based magnets, thus far, and is comparable to the room-temperature value of forced-volume magnetostriction in invar alloys. Cr2Te3 shows a large delta V/V of 680 ppm when applying a magnetic field of 9 T at 200 K. Both samples display particularly large volume increases around the Curie temperature, where they also show negative thermal expansion due to the microstructural effects, suggesting that the cooperation between anisotropic lattice deformation associated with the magnetic ordering and microstructural effects is essential for the manifestation of the large magnetic-field-induced volume changes.

    DOI: 10.1063/5.0134911

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  10. Mechanism of Reductive Fluorination by PTFE-Decomposition Fluorocarbon Gases for WO<sub>3</sub> Reviewed

    Yamamoto, H; Tada, K; Hwang, J; Hirai, D; Hiroi, Z; Matsumoto, K; Hagiwara, R

    INORGANIC CHEMISTRY   Vol. 62 ( 5 ) page: 2116 - 2127   2023.1

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

    Reductive fluorination, which entails the substitution of O2- from oxide compounds with F- from fluoropolymers, is considered a practical approach for preparing transition-metal oxyfluorides. However, the current understanding of the fundamental reaction paths remains limited due to the analytical complexities posed by high-temperature reactions in glassware. Therefore, to expand this knowledgebase, this study investigates the reaction mechanisms behind the reductive fluorination of WO3 using polytetrafluoroethylene (PTFE) in an Ni reactor. Here, we explore varied reaction conditions (temperature, duration, and F/W ratio) to suppress the formation of carbon byproducts, minimize the dissipation of fluorine-containing tungsten (VI) compounds, and achieve a high fluorine content. The gas-solid reaction paths are analyzed using infrared spectroscopy, which revealed tetrafluoroethylene (C2F4), hexafluoropropene (C3F6), and iso-octafluoroisobutene (i-C4F8) to be the reactive components in the PTFE-decomposition gas during the reactions with WO3 at 500 °C. CO2 and CO are further identified as gaseous byproducts of the reaction evincing that the reaction is prompted by difluorocarbene (:CF2) formed after the cleavage of CâÂÂC bonds in i-C4F8, C3F6, and C2F4 upon contact with the WO3 surface. The solid-solid reaction path is established through a reaction between WO3 and WO3-xFx where solid-state diffusion of O2- and F- is discerned at 500 °C.

    DOI: 10.1021/acs.inorgchem.2c03761

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  11. Crystallization of heavy fermions via epitaxial strain in spinel LiV<inf>2</inf>O<inf>4</inf>thin film Reviewed

    Niemann U., Wu Y.M., Oka R., Hirai D., Wang Y., Eren Suyolcu Y., Kim M., Van Aken P.A., Takagi H.

    Proceedings of the National Academy of Sciences of the United States of America   Vol. 120 ( 24 ) page: e2215722120   2023

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Proceedings of the National Academy of Sciences of the United States of America  

    The mixed-valent spinel LiV2O4 is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has remained yet elusive. A charge-ordering (CO) instability of V3+ and V4+ ions that is geometrically frustrated by the V pyrochlore sublattice from forming a long-range CO down to T = 0 K has been proposed as a prime candidate for the mechanism. Here, we uncover the hidden CO instability by applying epitaxial strain on single-crystalline LiV2O4 thin films. We find a crystallization of heavy fermions in a LiV2O4 film on MgO, where a charge-ordered insulator comprising of a stack of V3+ and V4+ layers along [001], the historical Verwey-Type ordering, is stabilized by the in-plane tensile and out-of-plane compressive strains from the substrate. Our discovery of the [001] Verwey-Type CO, together with previous realizations of a distinct [111] CO, evidence the close proximity of the heavy-fermion state to degenerate CO states mirroring the geometrical frustration of the V pyrochlore lattice, which supports the CO instability scenario for the mechanism behind the heavy-fermion formation.

    DOI: 10.1073/pnas.2215722120

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  12. Electronic Properties of Pyrochlore-Type Ca2Ir2O7 Reviewed International journal

    Yuki Nakayama, Yoshihiko Okamoto, Daigorou Hirai, Koshi Takenaka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 91 ( 12 )   2022.12

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    The electrical resistivity, magnetic susceptibility, and heat capacity of sintered samples of Ca2Ir2O7, in which pentavalent Ir atoms with 5d4 electron configuration form a pyrochlore structure, have been studied. The obtained experimental data strongly suggest that Ca2Ir2O7 is metallic below room temperature and exhibits no electronic or magnetic phase transitions above 0.12 K.

    DOI: 10.7566/JPSJ.91.125002

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  13. Anisotropic magnetic phase diagram of geometrically frustrated iridate Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub> Reviewed

    Hanate, H; Hirai, D; Hiroi, Z; Matsuhira, K

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 564   2022.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Magnetism and Magnetic Materials  

    We report magnetic properties of single-crystal Ca5Ir3O12 having a hexagonal noncentrosymmetric structure. We measured the anisotropy of the magnetic phase transition at 7.8 K up to 70 kOe and obtained magnetic phase diagrams parallel and perpendicular to the c-axis. The magnetic phase diagrams showed that the transition temperature was gradually suppressed on application of a magnetic field to perpendicular to the c-axis. In contrast, the transition temperature was increased when a magnetic field of up to 70 kOe was applied to the c-axis. We examined this enhancement in the magnetic transition temperature along the c-axis. From these features of the observed magnetic properties, possibility of multipole magnetic ordering was examined.

    DOI: 10.1016/j.jmmm.2022.170072

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  14. Dimensional reduction and incommensurate dynamic correlations in the $$S=\frac{1}{2}$$ triangular-lattice antiferromagnet Ca3ReO5Cl2 Reviewed International coauthorship International journal

    S. A. Zvyagin, A. N. Ponomaryov, J. Wosnitza, D. Hirai, Z. Hiroi, M. Gen, Y. Kohama, A. Matsuo, Y. H. Matsuda, K. Kindo

    Nature Communications   Vol. 13 ( 1 ) page: 6310   2022.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    Abstract

    The observation of spinon excitations in the $$S=\frac{1}{2}$$ triangular antiferromagnet Ca<sub>3</sub>ReO<sub>5</sub>Cl<sub>2</sub> reveals a quasi-one-dimensional (1D) nature of magnetic correlations, in spite of the nominally 2D magnetic structure. This phenomenon is known as frustration-induced dimensional reduction. Here, we present high-field electron spin resonance spectroscopy and magnetization studies of Ca<sub>3</sub>ReO<sub>5</sub>Cl<sub>2</sub>, allowing us not only to refine spin-Hamiltonian parameters, but also to investigate peculiarities of its low-energy spin dynamics. We argue that the presence of the uniform Dzyaloshinskii-Moriya interaction (DMI) shifts the spinon continuum in momentum space and, as a result, opens a zero-field gap at the Γ point. We observed this gap directly. The shift is found to be consistent with the structural modulation in the ordered state, suggesting this material as a perfect model triangular-lattice system, where a pure DMI-spiral ground state can be realized.

    DOI: 10.1038/s41467-022-33992-5

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    Other Link: https://www.nature.com/articles/s41467-022-33992-5

  15. Characterization of the charge transfer luminescence of the [WO<sub>6</sub>]<SUP>6-</SUP> octahedron in Ca<sub>3</sub>WO<sub>6</sub> and the [WO<sub>5</sub>]<SUP>4-</SUP> square pyramid in Ca<sub>3</sub>WO<sub>5</sub>Cl<sub>2</sub> Reviewed

    Kitagawa, Y; Takemura, S; Hirai, D; Hiroi, Z; Ueda, J; Tanabe, S

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   Vol. 24 ( 39 ) page: 24203 - 24211   2022.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Chemistry Chemical Physics  

    Charge transfer (CT) luminescence of different types of polyhedra, [WO5]4− in Ca3WO5Cl2 and [WO6]6− in Ca3WO6, is characterized by spectroscopic experiments and ab initio calculations. According to the geometry optimization, W6+ ions form five-fold [WO5]4− square pyramids in Ca3WO5Cl2 because of a large interatomic distance between W6+ and Cl− of 3.266 Å. The analysis of the density of electronic states reveals the ionic character of Cl− ions to the W6+ ions in the Ca3WO5Cl2 lattice, resulting in the observed broad luminescence band peak at 488 nm of the single-crystal Ca3WO5Cl2 sample being assigned to the CT transition in the [WO5]4− square pyramid. Compared with the [WO6]6− octahedron in Ca3WO6, the [WO5]4− square pyramid shows an inconsistent CT energy shift: higher CT absorption and lower luminescence energies. The larger bandgap brings about higher absorption energy due to the structural and compositional features of the orthorhombic Ca3WO5Cl2. The redshifted CT luminescence band and small activation energy for the thermal quenching of the Ca3WO5Cl2 sample are explained, assuming that the CT states of the anisotropic [WO5]4− square pyramid take a larger offset in the configurational coordinate diagram than the [WO6]6− octahedron.

    DOI: 10.1039/d2cp02753d

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  16. Linear Trimer Molecule Formation by Three-Center-Four-Electron Bonding in a Crystalline Solid RuP Reviewed International journal

    Daigorou Hirai, Keita Kojima, Naoyuki Katayama, Mitsuaki Kawamura, Daisuke Nishio-Hamane, Zenji Hiroi

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   Vol. 144 ( 39 ) page: 17857 - 17864   2022.10

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

    Some inorganic solids undergo phase transitions that result in the formation of ???molecules??? in their crystalline frameworks, which are frequently accompanied by dramatic changes in physical properties; the metal???insulator transition (MIT) in vanadium dioxide, for instance, is accompanied by the formation of dimer molecules with conventional two-center???two-electron bonding. We have discovered the creation of a linear ruthenium trimer with atypical three-center???four-electron bonding in ruthenium monophosphide at its MIT. Our detailed structural investigation and electronic structure calculations reveal that charge transfer from polymerized phosphorous to ruthenium automatically tunes the electron density to precisely four per trimer at the MIT, with all conduction electrons present at high temperatures being trapped by the trimer???s molecular orbitals at low temperatures. Our results demonstrate that molecules are essential even in solid crystals, as they impact their electronic properties.<comment>Superscript/Subscript Available</comment

    DOI: 10.1021/jacs.2c06173

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  17. Quadrupole Fluctuation Effect on Magnetic Torque for Hourglass Dirac Loop Chain Metal β-ReO<inf>2</inf> Reviewed

    Shinya Uji, Taichi Terashima, Daigorou Hirai, Takahito Anbai, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 91 ( 8 )   2022.8

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    Magnetic torque measurements have been performed to investigate the electronic state of the metallic β-phase ReO2 with Dirac nodal lines forming a loop chain. The sinusoidal torque curves as a function of the field angle with a two-fold symmetry are observed in the whole temperature region. The amplitude quadratically increases with field at high temperatures, which is recognized as the conventional Pauli paramagnetic behavior. As temperature decreases, the amplitude steeply increases and the nonlinear magnetization becomes evident especially for the field in the ac plane. The analyses based on Landau theory show that the change of the torque signal is ascribed to electric quadrupole fluctuations. The anisotropic susceptibility due to the quadrupole fluctuations is strongly enhanced toward 0K and 0 T, suggesting quantum critical behavior in the vicinity of a quantum critical point.

    DOI: 10.7566/JPSJ.91.084702

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  18. Crystal structure and superconductivity of NaAlSi<sub>1–x </sub>Ge<sub> x </sub> single crystals Reviewed

    Takahiro Yamada, Daigorou Hirai, Toshiya Ikenobe, Hisanori Yamane, Zenji Hiroi

    Journal of Physics: Conference Series   Vol. 2323 ( 1 ) page: 012004 - 012004   2022.8

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

    Abstract

    NaAlSi and NaAlGe are nodal-line semimetals with an anti-PbFCl type structure. The former is a superconductor with a transition temperature T<sub>c</sub> of 7 K, while the latter does not exhibit superconductivity. We prepared single crystals of solid solution NaAlSi<sub>1–x</sub>Ge<sub>x</sub> by the Na–Ga flux method and investigated their crystal structures and superconductivity by X-ray structural analysis and magnetization measurements, respectively. The crystal structure parameters vary continuously with x, while the T<sub>c</sub> initially decreases gradually from 6.9 K for x = 0 to 5.6 K for x = 0.33 and then decreases rapidly to below 1.8 K for x = 0.45. This sudden variation in T<sub>c</sub> at x ~ 0.4 may not be explained by the decrease in phonon frequency due to the Ge substitution, but suggests an unusual change in the electronic structure, in spite that the calculated band structures of the end members are almost identical with nearly equal density of states.

    DOI: 10.1088/1742-6596/2323/1/012004

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    Other Link: https://iopscience.iop.org/article/10.1088/1742-6596/2323/1/012004/pdf

  19. Pseudogap Formation in the Nodal-Line Semimetal NaAlGe Reviewed

    Takahiro Yamada, Daigorou Hirai, Tamio Oguchi, Hisanori Yamane, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 91 ( 7 )   2022.7

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

    DOI: 10.7566/JPSJ.91.074801

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  20. Fermi surface and mass enhancement in the topological nodal-line semimetal NaAlSi Reviewed

    Shinya Uji, Takako Konoike, Yuya Hattori, Taichi Terashima, Tamio Oguchi, Takahiro Yamada, Daigorou Hirai, Zenji Hiroi

    Physical Review B   Vol. 105 ( 23 )   2022.6

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

    Quantum oscillations in the magnetic torque for the topological nodal-line semimetal NaAlSi with a superconducting transition at Tc=7K have been measured to investigate the Fermi surface. Four oscillation branches, α, β, γ, and δare observed, whose frequency ranges from 40 to 380 T in magnetic fields parallel to the c axis. The results are consistent with the present first-principles band calculations, showing the presence of small Fermi surfaces elongated in the kz direction. We obtain the large mass enhancement factors 2.0 for α and 3.1 for γ, ascribed to many-body effects likely responsible for the superconductivity. A nontrivial Berry phase is obtained for α, arising from the linear dispersion of the energy band.

    DOI: 10.1103/PhysRevB.105.235103

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.105.235103/fulltext

  21. Pyrochlore oxide Hg2Os2O7 on verge of metal–insulator boundary Reviewed

    Kota Kataoka, Daigorou Hirai, Akihiro Koda, Ryosuke Kadono, Takashi Honda, Zenji Hiroi

    Journal of Physics: Condensed Matter   Vol. 34 ( 13 ) page: 135602 - 135602   2022.3

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

    <title>Abstract</title>
    Semimetallic osmium pyrochlore oxide Cd<sub>2</sub>Os<sub>2</sub>O<sub>7</sub> undergoes a magnetic transition to an all-in–all-out (AIAO)-type order at 227 K, followed by a crossover to an AIAO insulator at around 210 K. Here, we studied the isostructural and isoelectronic compound Hg<sub>2</sub>Os<sub>2</sub>O<sub>7</sub> through thermodynamic measurements, muon spin rotation (μSR) spectroscopy and neutron diffraction experiments. A similar magnetic transition, probably to an AIAO-type order, was observed at 88 K, while the resistivity showed a decrease at the transition and remained metallic down to 2 K. Thus, the ground state of Hg<sub>2</sub>Os<sub>2</sub>O<sub>7</sub> is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd<sub>2</sub>Os<sub>2</sub>O<sub>7</sub>. Hg<sub>2</sub>Os<sub>2</sub>O<sub>7</sub> exists on the verge of the metal–insulator boundary on the metal side and provides an excellent platform for studying the electronic instability of 5<italic>d</italic> electrons with moderate electron correlations and strong spin–orbit interactions.

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  22. Unusual Resistive Transitions in the Nodal-Line Semimetallic Superconductor NaAlSi Reviewed

    Daigorou Hirai, Toshiya Ikenobe, Takahiro Yamada, Hisanori Yamane, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 91 ( 2 ) page: 024702   2022.2

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    DOI: 10.7566/JPSJ.91.024702

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  23. Dimer Crystallization Induced by Elemental Substitution in the Honeycomb Lattice of Ru1-xOsxCl3 Reviewed

    Kota Kataoka, Dirk Wulferding, Takeshi Yajima, Daisuke Nishio-Hamane, Daigorou Hirai, Seungyeol Lee, Kwang-Yong Choi, Zenji Hiroi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 91 ( 1 )   2022.1

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    Substitution effects of Os for Ru in alpha-RuCl3 are investigated in a wide composition range of 0 <= x <= 0.67 in Ru1-x-OsxCl3 by X-ray and electron diffraction, magnetic susceptibility, heat capacity, and Raman spectroscopy measurements. Apart from the Kitaev physics with antiferromagnetic interactions increasing with x, a rich phase diagram is obtained, which includes an antiferromagnetic long-range order below 12K for x <= 0.15, a dome-shaped spin-singlet dimer phase below 130 K for 0.15 <= x <= 0.40, and a magnetic short-range order for x > 0.40. A dimerization as similarly observed in a-RuCl3 under high pressure occurs in the spin-singlet phase. It is suggested that Ru Os pairs in the solid solutions tend to form dimers with short bonds and trigger the first-order transition in the presence of pseudo-threefold rotational symmetry for dimerization around a substituted Os atom only at low substitutions. This is a rare example of molecular orbital crystallization induced by elemental substitution in a highly disordered system. The short-range order at high substitutions may be related to a random-singlet state stabilized by bond disorder in the honeycomb net.

    DOI: 10.7566/JPSJ.91.014801

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  24. Interplay between Quadrupolar and Magnetic Interactions in 5<i>d</i>1 Double Perovskite Ba<sub>2</sub>MgReO<sub>6</sub> under Pressure Reviewed

    Arima, H; Oshita, Y; Hirai, D; Hiroi, Z; Matsubayashi, K

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 91 ( 1 )   2022.1

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    We measured the electrical resistivity, AC magnetic susceptibility, and specific heat of the cubic double perovskite Ba2MgReO6 under pressure. The application of pressure leads to a gradual increase in the transition temperature to the canted antiferromagnetic order, while the quadrupolar order is suppressed above ~5 GPa, at which a collinear antiferromagnetic state appears. The obtained unit cell volume-temperature phase diagram for the compound as well as the related compounds suggests that Ba2MgReO6 exists near the phase boundary between the noncollinear and the collinear antiferromagnetic order with multipole decrees of freedom.

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  25. Electronic states of metallic electric toroidal quadrupole order in Cd2Re2O7 determined by combining quantum oscillations and electronic structure calculations Reviewed

    Hishiro T. Hirose, Taichi Terashima, Daigorou Hirai, Yasuhito Matsubayashi, Naoki Kikugawa, David Graf, Kaori Sugii, Shiori Sugiura, Zenji Hiroi, Shinya Uji

    PHYSICAL REVIEW B   Vol. 105 ( 3 )   2022.1

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    Pyrochlore oxide Cd2Re2O7 exhibits successive structural transitions upon cooling that break its inversion symmetry. The low-temperature noncentrosymmetric metallic phases are believed to be some odd-parity multipole ordered states that are associated with a Fermi-liquid instability due to the strong spin-orbit interaction (SOI) and electronic correlation. However, their microscopic ordering pictures and the driving force of the phase transitions are still unclear. We determined the electronic structure of the lowest temperature phase of Cd2Re2O7 by combining quantum oscillation measurements with electronic structure calculations. The observed Fermi surfaces were well reproduced based on the optimized crystal structure, and we demonstrated the strong influence of the antisymmetric SOI. From the mass enhancement factor, we elucidated the strongly correlated nature of the electronic states. In addition, we visualized the microscopic picture of the 3z(2) - r(2)-type metallic electric-toroidal-quadrupole (ETQ) order characterized by the Re-O bond order. These results corroborate that the metallic ETQ order is driven by a Fermi-liquid instability associated with the strong SOI and electronic correlation, as has been theoretically proposed. Our results provide the basis for exploring unconventional phenomena expected in the metallic ETQ order.

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  26. Phase transition in the 5d1 double perovskite Ba2CaReO6 induced by high magnetic field Reviewed

    Hajime Ishikawa, Daigorou Hirai, Akihiko Ikeda, Masaki Gen, Takeshi Yajima, Akira Matsuo, Yasuhiro H. Matsuda, Zenji Hiroi, Koichi Kindo

    Physical Review B   Vol. 104 ( 17 )   2021.11

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    DOI: 10.1103/PhysRevB.104.174422

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  27. Pleochroic Crystal Exhibits Different Colors Depending on the Viewing Directions and Polarization of Light―Unique Properties of Mixed-Anion Compounds Reviewed

    Hirai Daigorou, Hiroi Zenji

    Butsuri   Vol. 76 ( 10 ) page: 658 - 662   2021.10

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    <p>Transition metal compounds sometimes exhibit attractive colors. These colors usually come from the excitation of the <i>d</i>-electrons by absorbing light. Unique <i>d</i>-orbital states may result in novel optical properties. A new 5<i>d</i> oxychloride, Ca<sub>3</sub>ReO<sub>5</sub>Cl<sub>2</sub>, shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. The key to realizing this unique optical property is found to be the mixed-anion coordination of the 5<i>d</i> rhenium ion, where five oxide ions are pyramidally coordinated and one chloride ion is located on the opposite side. This coordination activates the Laporute forbidden <i>d </i>–<i>d</i> transition and leads to non-degenerate 5<i>d</i> levels due to the complex crystal field. These features lead to polarization-dependent excitation of <i>d</i>-electrons, which is observed as pleochroism. The present results demonstrate that compounds containing more than one anionic species, called mixed-anion compounds, may have novel properties inaccessible to a single-anion analog owing to the characteristic crystal and electronic structures.</p>

    DOI: 10.11316/butsuri.76.10_658

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  28. Extremely large magnetoresistance in the hourglass dirac loop chain metal β-ReO<inf>2</inf> Reviewed

    Daigorou Hirai, Takahito Anbai, Shinya Uji, Tamio Oguchi, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 90 ( 9 )   2021.9

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    The transport and thermodynamic properties of β-ReO2 crystallizing in a nonsymmorphic structure were studied using high-quality single crystals. An extremely large magnetoresistance (XMR) of 22,000% was observed in a transverse magnetic field of 10 T at 2 K. However, unlike other topological semimetals that show XMR, β-ReO2 has a high electron carrier density of 1 × 1022 cm−3, as determined by Hall effect measurements and large Fermi surfaces in the electronic structure. In addition, a small Fermi surface with a small effective mass was evidenced by de Haas-van Alphen oscillation measurements. Previous band structure calculations [Wang, et al., Nat. Commun. 8, 1844 (2017)] revealed the existence of two types of loops made of Dirac points of hourglass-shaped dispersions that are connected to each other by a point to form a string of alternating loops, called a Dirac loop chain (DLC), which are protected by multiple glide symmetries. Our first-principles calculations revealed the complex Fermi surfaces, the smallest of which corresponds to the observed small Fermi surface, which is located near the DLC. The XMR of β-ReO2 is attributed to the small Fermi surface, which is likely caused by the DLC.

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  29. Organic Solvent-Free Process for the Rapid Fabrication of Nickel Ferrite-Reduced Graphene Oxide as a Magnetic Nanosorbent Using Supercritical Water Reviewed

    Osamu Sawai, Xiaoyun Zhou, Akira Yoko, Daigorou Hirai, Teppei Nunoura

    Industrial & Engineering Chemistry Research   Vol. 60 ( 27 ) page: 9897 - 9905   2021.7

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    DOI: 10.1021/acs.iecr.1c01424

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  30. Successive continuous phase transitions in spin–orbit coupled metal Cd<inf>2</inf>Re<inf>2</inf>O<inf>7</inf> Reviewed

    Shinya Uji, Hishiro T. Hirose, Taichi Terashima, Yasuhito Matsubayashi, Daigorou Hirai, Zenji Hiroi, Takumi Hasegawa

    Journal of the Physical Society of Japan   Vol. 90 ( 6 )   2021.6

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    A spin–orbit coupled metal Cd2Re2O7 is known to show two structural phase transitions at Ts1 ≈ 200 K and Ts2 ≈ 115 K, which are likely of an electronic origin. The magnetic torque curves have been measured as a function of the field angle near Ts2, which are decomposed into two terms, major twofold and minor fourfold symmetry terms. A steep but continuous change of the twofold term, associated with no significant hysteresis, is found below Ts2. The result shows a second order transition at Ts2 although it is prohibited from the view point of the crystal symmetry. The torque curve analyses propose possible successive transitions and point group symmetries below Ts2, which include an inverse symmetry breaking, a transition from a low to high symmetry phase with decreasing temperature.

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  31. Possible quadrupole order in tetragonal Ba2CdReO6 and chemical trend in the ground states of 5d 1 double perovskites Reviewed

    Daigorou Hirai, Zenji Hiroi

    Journal of Physics: Condensed Matter   Vol. 33 ( 13 ) page: 135603 - 135603   2021.3

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    DOI: 10.1088/1361-648X/abda79

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  32. Superconductivity in the Topological Nodal-line Semimetal NaAlSi Reviewed

    Takahiro Yamada, Daigorou Hirai, Hisanori Yamane, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 90 ( 3 ) page: 034710 - 034710   2021.3

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    DOI: 10.7566/JPSJ.90.034710

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  33. Superconducting state of nodal line semimetal NaAlSi studied by STM Reviewed

    Haze Masahiro, Sato Yudai, Yamada Takahiro, Yamane Hisanori, Hirai Daigorou, Hiroi Zenji, Hasegawa Yukio

    Abstract book of Annual Meeting of the Japan Society of Vacuum and Surface Science   Vol. 2021 ( 0 ) page: 1Ca06   2021

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    <p>Nodal line semimetals, whose valence and conduction bands cross on a line in the Brillouin zone, have attracted a lot of attention as a new class of topological materials. Recently it has been reported that NaAlSi is belong to nodal line semimetals and it shows superconducting transition at 7K, which is relatively high temperature. We will present the electronic properties of NaAlSi measured by low temperature scanning tunneling microscopy.</p>

    DOI: 10.14886/jvss.2021.0_1ca06

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  34. Domain control by adjusting anisotropic stress in pyrochlore oxide Cd<inf>2</inf>Re<inf>2</inf>O<inf>7</inf> Reviewed

    Tajima, S., Hirai, D., Kinoshita, Y., Tokunaga, M., Akiba, K., Kobayashi, T.C., Hirose, H.T., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 89 ( 11 )   2020.11

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    The 5d pyrochlore oxide Cd2Re2O7 exhibits successive phase transitions from a cubic pyrochlore structure (phase I) to a tetragonal structure without inversion symmetry below T-s1 of similar to 200K (phase II) and further to another noncentrosymmetric tetragonal structure below T-s2 of similar to 120K (phase III). The two low-temperature phases may be characterized by odd-parity multipolar orders induced by the Fermi liquid instability of the spin-orbit-coupled metal. To control the tetragonal domains generated by the transitions and to obtain a single-domain crystal for the measurements of anisotropic properties, we prepared single crystals with the (001) surface and applied biaxial and uniaxial stresses along the plane. Polarizing optical microscopy observations revealed that inducing a small strain of approximately 0.05% could flip the twin domains ferroelastically in a reversible fashion at low temperatures, which evidences that the tetragonal deformation switches at T-s2 between c > a for phase II and c < a for phase III. Resistivity measurements using single-domain crystals under uniaxial stress showed that the anisotropy was maximum at around T-s2 and turned over across T-s2: resistivity along the c axis is larger (smaller) than that along the a axis by similar to 25% for phase II (III) at around T-s2. These large anisotropies probably originate from spin-dependent scattering in the spin-split Fermi surfaces of the cluster electric toroidal quadrupolar phases of Cd2Re2O7.

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  35. Kitaev spin liquid candidate Os<inf>x</inf>Cl<inf>3</inf>comprised of honeycomb nano-domains Reviewed

    Kataoka, K., Hirai, D., Yajima, T., Nishio-Hamane, D., Ishii, R., Choi, K.-Y., Wulferding, D., Lemmens, P., Kittaka, S., Sakakibara, T., Ishikawa, H., Matsuo, A., Kindo, K., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 89 ( 11 ) page: 114709 - 114709   2020.11

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    DOI: 10.7566/JPSJ.89.114709

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  36. Bound spinon excitations in the spin- 12 anisotropic triangular antiferromagnet Ca3ReO5Cl2 Reviewed

    Kazuhiro Nawa, Daigorou Hirai, Maiko Kofu, Kenji Nakajima, Ryo Murasaki, Satoshi Kogane, Motoi Kimata, Hiroyuki Nojiri, Zenji Hiroi, Taku J. Sato

    Physical Review Research   Vol. 2 ( 4 )   2020.10

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    DOI: 10.1103/PhysRevResearch.2.043121

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  37. Anomalous changes of electric quadrupole order at low temperatures in the spin-orbit coupled metal Cd2Re2 O7 Reviewed

    Uji, S., Sugiura, S., Hirose, H.T., Terashima, T., Matsubayashi, Y., Hirai, D., Hiroi, Z., Hasegawa, T.

    Physical Review B   Vol. 102 ( 15 )   2020.10

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    DOI: 10.1103/PhysRevB.102.155131

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  38. Spin–orbit-coupled metal candidate PbRe<inf>2</inf>O<inf>6</inf> Reviewed

    Tajima, S., Hirai, D., Yajima, T., Nishio-Hamane, D., Matsubayashi, Y., Hiroi, Z.

    Journal of Solid State Chemistry   Vol. 288   2020.8

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    We study the lead rhenium oxide PbRe2O6 as a candidate spin-orbit-coupled metal (SOCM), which has attracted much attention as a testing ground for studying unconventional Fermi liquid instability associated with a large spin-orbit interaction. The compound comprises a stack of modulated honeycomb lattices made of Re5+ (5d(2)) ions in a centrosymmetric R-3m structure at room temperature. Resistivity, magnetic susceptibility, and heat capacity measurements using single crystals reveal two successive first-order phase transitions at T-s1= 265 K and T-s2 = 123 K. At T sb the magnetic susceptibility is enormously reduced and a structural transition to a monoclinic structure takes place, while relatively small changes are observed at T-s2. Surprisingly, PbRe2O6 bears a close resemblance to another SOCM candidate Cd2Re2O7 despite crucial differences in the crystal structure and probably in the electronic structure, suggesting that PbRe2O6 is an SOCM.

    DOI: 10.1016/j.jssc.2020.121359

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  39. Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A<inf>3</inf>ReO<inf>5</inf>Cl<inf>2</inf>(A = Ba, Sr) Reviewed

    Hirai, D., Yajima, T., Nawa, K., Kawamura, M., Hiroi, Z.

    Inorganic Chemistry   Vol. 59 ( 14 ) page: 10025 - 10033   2020.7

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    DOI: 10.1021/acs.inorgchem.0c01187

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  40. Antiferromagnetic long-range order in the 5d1 double-perovskite Sr2MgReO6 Reviewed

    Gao, S., Hirai, D., Sagayama, H., Ohsumi, H., Hiroi, Z., Arima, T.-H.

    Physical Review B   Vol. 101 ( 22 )   2020.6

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    DOI: 10.1103/PhysRevB.101.220412

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  41. Detection of multipolar orders in the spin-orbit-coupled 5d Mott insulator Ba2MgReO6 Reviewed International coauthorship International journal

    Daigorou Hirai, Hajime Sagayama, Shang Gao, Hiroyuki Ohsumi, Gang Chen, Taka-hisa Arima, Zenji Hiroi

    Physical Review Research   Vol. 2 ( 2 )   2020.6

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    DOI: 10.1103/PhysRevResearch.2.022063

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  42. Coexistence of odd-parity and even-parity order parameters in the multipole order phase of the spin-orbit coupled metal C d<inf>2</inf> R e<inf>2</inf> O<inf>7</inf> Reviewed

    Matsubayashi, Y., Sugii, K., Hirai, D., Hiroi, Z., Hasegawa, T., Sugiura, S., Hirose, H.T., Terashima, T., Uji, S.

    Physical Review B   Vol. 101 ( 20 )   2020.5

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    Magnetic torque measurements have been performed to investigate the phase transitions of the metallic pyrochlore compound Cd2Re2O7, in which a spin-orbit (SO) interaction leads to unique multipole orders associated with an inversion symmetry breaking. We find that the magnetic torque signals with a fourfold symmetry (τ4- H4) as well as a twofold symmetry (τ2- H2) are significantly enhanced at low temperatures below a structural phase transition temperature (∼200 K). The analyses of the torque curve symmetries show that the τ4 term arises from an even-parity order parameter (OP) with the irreducible representation Eg, whereas the τ2 term from an odd-parity OP with Eu, T1u or T2u. The parity mixing of the primary OPs shows a peculiar phase transition in the SO coupled Cd2Re2O7. The coexistence of the two OPs provides important insights into the origin of the multipole orders induced by the SO interaction.

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  43. Variation in Superconducting Symmetry Against Pressure on Noncentrosymmetric Superconductor Cd2Re2O7 Revealed by 185/187Re Nuclear Quadrupole Resonance Reviewed

    Shunsaku Kitagawa, Kenji Ishida, Tatsuo C. Kobayashi, Yasuhito Matsubayashi, Daigorou Hirai, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 89 ( 5 )   2020.5

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    We performed Re-185/187 nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd2Re2O7 under various crystal structures. The pressure dependence of superconducting transition temperature T-c determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [Kobayashi et al., J. Phys. Soc. Jpn. 80, 023715 (2011)]. Below 2.2 GPa, in the nuclear spin-lattice relaxation rate 1/T-1, a clear coherence peak was observed just below T-c, indicating conventional s-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the p-wave dominant state against pressure.

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  44. Observation of metal to nonmagnetic insulator transition in polycrystalline RuP by photoemission spectroscopy Reviewed

    Daiki Ootsuki, Kei Sawada, Hiroki Goto, Daigorou Hirai, Daisuke Shibata, Masato Kawamoto, Akira Yasui, Eiji Ikenaga, Masashi Arita, Hirofumi Namatame, Masaki Taniguchi, Tatsuya Toriyama, Takehisa Konishi, Yukinori Ohta, Naurang L. Saini, Teppei Yoshida, Takashi Mizokawa, Hidenori Takagi

    Physical Review B   Vol. 101 ( 16 )   2020.4

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    DOI: 10.1103/PhysRevB.101.165113

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  45. Structure analysis and electrical resistivity of the high- And lowerature phases of NaPd<inf>3</inf>Ge<inf>2</inf> single crystal Reviewed

    Yamada, T., Aiba, K., Hirai, D., Hiroi, Z., Yamane, H.

    Japanese Journal of Applied Physics   Vol. 59 ( SF ) page: SFFC03 - SFFC03   2020.4

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    DOI: 10.7567/1347-4065/ab65ab

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  46. Na<inf>3</inf>Pt<inf>10</inf>Si<inf>5</inf>: A Non-Centrosymmetric Superconductor Having Rattling Na Atoms in the Tunnel Framework Structure Reviewed

    Yamada, T., Hirai, D., Hiroi, Z., Yamane, H.

    Inorganic Chemistry   Vol. 58 ( 19 ) page: 12911 - 12917   2019.10

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    DOI: 10.1021/acs.inorgchem.9b01869

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  47. Successive symmetry breaking in a J<inf>eff</inf> = 3=2 quartet in the spin–orbit coupled insulator Ba<inf>2</inf>MgReO<inf>6</inf> Reviewed

    Hirai, D., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 88 ( 6 )   2019.6

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    DOI: 10.7566/JPSJ.88.064712

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  48. Weak Anisotropic Lithium-Ion Conductivity in Single Crystals of Li<inf>10</inf>GeP<inf>2</inf>S<inf>12</inf> Reviewed

    Iwasaki, R., Hori, S., Kanno, R., Yajima, T., Hirai, D., Kato, Y., Hiroi, Z.

    Chemistry of Materials   Vol. 31 ( 10 ) page: 3694 - 3699   2019.5

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    Single crystals of the lithium-ion conductor Li10GeP2S12 have been successfully grown by the self-flux method and are studied by means of X-ray diffraction and impedance spectroscopy. The weak anisotropic ionic conductivity is observed to be 27 and 7 mS cm(-1) in the [001] and [110] directions, respectively, at room temperature. Markedly, however, the activation energies are nearly equal, approximately 0.3 eV, in the two directions, which means that common diffusion paths along [110] dominate the long-range diffusion in Li10GeP2S12.

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  49. One-dimensionalization by Geometrical Frustration in the Anisotropic Triangular Lattice of the 5d Quantum Antiferromagnet Ca3ReO5Cl2 Reviewed

    Daigorou Hirai, Kazuhiro Nawa, Mitsuaki Kawamura, Takahiro Misawa, Zenji Hiroi

    Journal of the Physical Society of Japan   Vol. 88 ( 4 ) page: 044708 - 044708   2019.4

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    We report on the emergence of antiferromagnetic spin chains from two-dimensionally aligned spins on the anisotropic triangular lattice (ATL) in the insulating calcium rhenium oxychloride Ca3ReO5Cl2. The compound contains Re6+ ions, each with one unpaired electron in the d(xy) orbital, which are arranged to form a spin-1/2 ATL with J'/J similar to 0.32 and J = 41 K, where J and J' are magnetic interactions in and between the chains, respectively. In spite of the apparent two-dimensionality, we observe clear evidence of a gapless spin liquid that is characteristic of the spin-1/2 Heisenberg chain. This one-dimensionalization must be caused by geometrical frustration: growing antiferromagnetic correlations in every chain effectively cancel out interchain zigzag couplings at low temperatures. Ca3ReO5Cl2 provides us with a detailed insight into the interesting physics of the An antiferromagnet, especially via comparison with the typical ATL compound Cs2CuCl4.

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  50. Non-reciprocal magneto resistance in Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> Reviewed

    Kimata Motoi, Sudo Kenta, Hirai Daigorou, Matsubayashi Yasuhito, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 74.2 ( 0 ) page: 2013 - 2013   2019

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    DOI: 10.11316/jpsgaiyo.74.2.0_2013

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  51. Domain control of the pyrochlore oxide Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> by uniaxial strain Reviewed

    Tajima Satoshi, Hirai Daigorou, Kinoshita Yuto, Tokunaga Masashi, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 74.1 ( 0 ) page: 2382 - 2382   2019

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    DOI: 10.11316/jpsgaiyo.74.1.0_2382

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  52. Synthesis and physical properties of Kitaev spin liquid candidate OsCl<sub>3</sub> Reviewed

    Kataoka K., Hirai D., Yajima T., Hamane D., Kittaka S., Sakakibara T., Hiroi Z.

    Meeting Abstracts of the Physical Society of Japan   Vol. 74.1   page: 2313 - 2313   2019

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    DOI: 10.11316/jpsgaiyo.74.1.0_2313

  53. Formation and control of twin domains in the pyrochlore oxide Cd<inf>2</inf>Re<inf>2</inf>O<inf>7</inf> Reviewed

    Matsubayashi, Y., Hirai, D., Tokunaga, M., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 87 ( 10 )   2018.10

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    The successive phase transitions of the pyrochlore oxide Cd2Re2O7 are studied<br />
    by polarizing microscopy and magnetic susceptibility measurements. The<br />
    formation of twin domains is visualized in the polarizing images of a pristine<br />
    (111) crystal surface upon cooling through the cubic-to-tetragonal transition<br />
    at Ts1 ~ 200 K. Moreover, a dramatic change in the twinning pattern is observed<br />
    at Ts2 ~120 K, which suggests that the tetragonal c axis flips as the strain<br />
    changes its direction at the tetragonal-to-tetragonal transition. Magnetic<br />
    susceptibility measurements reveal significant domain alignment upon cooling<br />
    across Ts1 and Ts2 in a magnetic field of 7 T, which are due to ~10% anisotropy<br />
    in the magnetic susceptibility for the low-temperature phases. Interestingly,<br />
    the anisotropy is reversed at Ts2: \c{hi}c &lt; \c{hi}a above Ts2 and vice versa<br />
    below Ts2.

    DOI: 10.7566/JPSJ.87.104604

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  54. Split Fermi Surfaces of the Spin–Orbit-Coupled Metal Cd<inf>2</inf>Re<inf>2</inf>O<inf>7</inf> Probed by de Haas–van Alphen Effect Reviewed

    Matsubayashi, Y., Sugii, K., Hirose, H.T., Hirai, D., Sugiura, S., Terashima, T., Uji, S., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 87 ( 5 ) page: 053702   2018.5

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    The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition with inversion symmetry breaking (ISB) at T-s1 = 200 K. A recent theory [L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic instability that leads to a multipolar order in the spin-orbit-coupled metal. To observe the Fermi surface of the low-temperature phase of Cd2Re2O7, we perform de Haas-van Alphen effect measurements by means of magnetic torque. In reference to a calculated band structure, the spin-split Fermi surfaces with large cyclotron masses of 5-9m(0) are revealed. The splitting is suggested to be due to an antisymmetric spin-orbit coupling induced by ISB, the strength of which is estimated to be approximately 67 K, which is rather smaller than those of typical non-centrosymmetric metals.

    DOI: 10.7566/JPSJ.87.053702

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  55. Facile synthetic route to transition metal oxyfluorides via reactions between metal oxides and PTFE Reviewed

    Hirai, D., Sawai, O., Nunoura, T., Hiroi, Z.

    Journal of Fluorine Chemistry   Vol. 209   page: 43 - 48   2018.5

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    Inorganic oxyfluorides have significant importance in the development of new functionalities for energy production and storage, photonics, catalysis, etc. In order to explore a simple preparation route that avoids the use of toxic HF or F2 gas as a reaction reagent, we have employed polytetrafluoroethylene (PTFE). Five oxyfluorides including Nb5O12F, Nb3O7F, Ta3O7F, TaO2F, and Mo4O11.2F0.8 were synthesized by reactions between PTFE and transition metal oxides in sealed quartz ampules. The reaction mechanism was studied by means of gas analysis, which detected SiF4 as a main product gas during the reaction. A possible reaction mechanism between the PTFE and transition metal oxides is discussed.

    DOI: 10.1016/j.jfluchem.2018.02.008

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  56. Pyrochlore Oxide Superconductor Cd<inf>2</inf>Re<inf>2</inf>O<inf>7</inf> Revisited Reviewed

    Hiroi, Z., Yamaura, J.-I., Kobayashi, T.C., Matsubayashi, Y., Hirai, D.

    Journal of the Physical Society of Japan   Vol. 87 ( 2 )   2018.2

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    The superconducting pyrochlore oxide Cd2Re2O7 is revisited with a particular emphasis on the sample-quality issue. The compound has drawn attention as the only superconductor (Tc = 1.0 K) that has been found in the family of α-pyrochlore oxides since its discovery in 2001. Moreover, it exhibits two characteristic structural transitions from the cubic pyrochlore structure, with the inversion symmetry broken at the first one at 200 K. Recently, it has attracted increasing attention as a candidate spin–orbit coupled metal (SOCM), in which specific Fermi liquid instability is expected to lead to an odd-parity order with spontaneous inversion-symmetry breaking [L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] and parity-mixing superconductivity [V. Kozii and L. Fu, Phys. Rev. Lett. 115, 207002 (2015)
    Y. Wang et al., Phys. Rev. B 93, 134512 (2016)]. We review our previous experimental results in comparison with those of other groups in the light of the theoretical prediction of the SOCM, which we consider meaningful and helpful for future progress in understanding this unique compound.

    DOI: 10.7566/JPSJ.87.024702

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  57. Nonlinear conductivity of geometrically frustrated iridate Ca<inf>5</inf>Ir<inf>3</inf>O<inf>12</inf> Reviewed

    Matsuhira, K., Nakamura, K., Yasukuni, Y., Yoshimoto, Y., Hirai, D., Hiroi, Z.

    Journal of the Physical Society of Japan   Vol. 87 ( 1 )   2018.1

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    We report the discovery of nonlinear conductivity along the c-axis in a single crystal of Ca5Ir3O12, which indicates a semiconducting behavior with a narrow band gap of similar to 0.2 eV. The resistivity decreases with increase in the applied current. This nonlinearity is reversible with the direction of current. We also show the ab initio density functional band structures and the Fermi surface. We found that the spin-orbit interactions result in an appreciable change in the low-energy electronic structure; the interaction splits the metallic bands and leads to a pocket-like band structure, thus reducing the metallic trend. The size of the spin-orbit interaction is estimated as similar to 0.3 eV, which is large enough to be comparable to the valence bandwidth of similar to 0.5 eV. The Fermi surface exhibits a sheet structure along the c*-axis, due to the 1D chain structure of edge-sharing IrO6.

    DOI: 10.7566/JPSJ.87.013703

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  58. Synthesis of anti-perovskite-type carbides and nitrides from metal oxides and melamine Reviewed

    Hirai, D., Tanaka, H., Nishio-Hamane, D., Hiroi, Z.

    RSC Advances   Vol. 8 ( 73 ) page: 42025 - 42031   2018

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    Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are synthesised through reactions between metal oxides and organic compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by choosing different reaction temperatures and nominal oxide-to-melamine ratios. SnNCo3 is synthesised for the first time by this melamine method. Resistivity, magnetisation, and heat capacity measurements reveal that SnNCo3 is a correlated metal with a high density of states at the Fermi level. The results demonstrate that this feasible synthetic route using melamine is useful in the search for complex metal carbides and nitrides toward novel functional materials.

    DOI: 10.1039/c8ra07581f

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  59. Observation of current rectification in Cd2Re2O7 Reviewed

    Kimata Motoi, Matsubayashi Yasuhito, Hiroi Daigorou, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 73.2 ( 0 ) page: 1408 - 1408   2018

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    DOI: 10.11316/jpsgaiyo.73.2.0_1408

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  60. Crystal growth and tetragonal domain structure in the superconducting pyrochlore oxide Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> Reviewed

    Matsubayashi Yasuhito, Hirai Daigorou, Hamane Daisuke, Tokunaga Masashi, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 73.1   page: 2303 - 2303   2018

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    DOI: 10.11316/jpsgaiyo.73.1.0_2303

  61. Domain Formation and Control in the Pyrochlore Oxide Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> Reviewed

    Matsubayashi Yasuhito, Hirai Daigorou, Tokunaga Masashi, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 73.2 ( 0 ) page: 1405 - 1405   2018

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    DOI: 10.11316/jpsgaiyo.73.2.0_1405

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  62. Angular dependent magneto resistance in Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub> Reviewed

    Kimata Motoi, Matsubayashi Yasuhito, Hirai Daigoro, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 73.1 ( 0 ) page: 2302 - 2302   2018

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    DOI: 10.11316/jpsgaiyo.73.1.0_2302

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  63. Nonlienar Conductivity of Geometrically Frustrated Iridate Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub> Reviewed

    Matsuhira K., Yoshida W., Yasukuni Y., Nakamura K., Yoshimoto Y., Hirai D., Hiroi Z.

    Meeting Abstracts of the Physical Society of Japan   Vol. 73.1 ( 0 ) page: 2044 - 2044   2018

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    DOI: 10.11316/jpsgaiyo.73.1.0_2044

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  64. “Visible” 5d Orbital States in a Pleochroic Oxychloride Reviewed

    Daigorou Hirai, Takeshi Yajima, Daisuke Nishio-Hamane, Changsu Kim, Hidefumi Akiyama, Mitsuaki Kawamura, Takahiro Misawa, Nobuyuki Abe, Taka-hisa Arima, Zenji Hiroi

    Journal of the American Chemical Society   Vol. 139 ( 31 ) page: 10784 - 10789   2017.8

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    Transition metal compounds sometimes exhibit attractive colors. Here, we report a new oxychloride, Ca3ReO5Cl2, that shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. This pleochroism is a consequence of the coincidental complex crystal field splitting of the 5d orbitals of the Re6+ ion in a square-pyramidal coordination of low symmetry in the energy range of the-visible spectrum. Since the relevant d-d transitions show characteristic polarization dependence according to the optical selection rule, the orbital states. are "visible" in Ca3ReO5Cl2.

    DOI: 10.1021/jacs.7b05128

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  65. Metal-insulator transition and magnetic fluctuations in polycrystalline Ru1-x Rhx P investigated by P 31 NMR Reviewed International journal

    Li, S., Kobayashi, Y., Itoh, M., Hirai, D., Takagi, H.

    Physical Review B   Vol. 95 ( 15 )   2017.4

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    P-31 NMR measurements have been made on polycrystalline samples to study a metal-insulator (MI) transition and magnetic fluctuations in Ru1-xRhxP which has metallic (M), pseudogap (PG), insulating (I), and superconducting (SC) phases. We find that RuP undergoes a crossover from the high-temperature (high-T) M phase to the PG phase with the pseudo spin-gap behavior probed by the nuclear spin-lattice relaxation rate at T-PG = 330 K. The first-orderMI transition is observed to take place from the PG phase to the low-T nonmagnetic I phase with the spin-gap energy of 1250 K at T-MI = 270 K. In the PG phase of Ru1-xRhx P with 0 &lt;= x&lt; 0.45, an analysis based on the modifiedKorringa relation, which is applicable to an itinerant paramagnetwith weak electron correlation, shows that antiferromagnetic (AFM) fluctuations described in the random-phase approximation are enhanced in the low-T and low-x region. Around the PG-M phase boundary at xc similar to 0 .45, there is the SC phase whose normal state has negligible electron-electron interaction. We discuss the MI transition, the crossover from the M phase to the PG phase, and the magnetic properties of each phase based on the band structure.

    DOI: 10.1103/PhysRevB.95.155137

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  66. Magnetic ground state of 5d pyrochlore oxide Hg<sub>2</sub>Os<sub>2</sub>O<sub>7</sub> investigated by muSR technique Reviewed

    Koda A., Okabe H., Hiraishi M., Takeshita S., Kojima K. M., Kadono R., Kataoka K., Hirai D., Hiroi Z.

    Meeting Abstracts of the Physical Society of Japan   Vol. 72   page: 1794 - 1794   2017

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    DOI: 10.11316/jpsgaiyo.72.2.0_1794

  67. Magnetism and electrical conductivity of the Geometrically Frustrated Iridate Ca5Ir3O12 Reviewed

    Matsuhira K., Yasukuni Y., Nakamura K., Yoshimoto Y., Hirai D., Hiroi Z.

    Meeting Abstracts of the Physical Society of Japan   Vol. 72.2 ( 0 ) page: 1788 - 1788   2017

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    DOI: 10.11316/jpsgaiyo.72.2.0_1788

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  68. Semimetallic transport properties of epitaxially stabilized perovskite CaIrO<inf>3</inf> films Reviewed

    Hirai, D., Matsuno, J., Nishio-Hamane, D., Takagi, H.

    Applied Physics Letters   Vol. 107 ( 1 ) page: 012104 - 012104   2015.7

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    We report on the synthesis and transport properties of perovskite (Pv) CaIrO3 thin films. The Pv phase of CaIrO3 was stabilized by epitaxial growth on SrTiO3, (LaAlO3)(0.3)(Sr2AlTaO6)(0.7), and LaAlO3 substrates with strong tensile, weak tensile, and compressive strains, respectively. The resistivity of these films showed a poorly metallic behavior. The Hall resistivity exhibited a sign change as a function of temperature and a nonlinear magnetic- field dependence, which clearly indicated the coexistence of electrons and holes and hence supported that Pv CaIrO3 films are semimetallic. The observed robustness of the semimetallic ground state against tensile and compressive strains is consistent with the presence of symmetry- protected Dirac points ( nodes) around the Fermi level that prohibits the system from becoming a band insulator. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4926723

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  69. Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics Reviewed

    Daigorou Hirai, Jobu Matsuno, Hidenori Takagi

    APL Materials   Vol. 3 ( 4 ) page: 041508 - 041508   2015.4

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    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects. (C) 2015 Author(s).

    DOI: 10.1063/1.4913389

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  70. Superconductivity at 3.7K in Ternary Silicide Li2IrSi3 Reviewed

    Daigorou Hirai, Rui Kawakami, Oxana V. Magdysyuk, Robert E. Dinnebier, Alexander Yaresko, Hidenori Takagi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 83 ( 10 )   2014.10

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    We report the discovery of superconductivity at T-c = 3.7K in the new ternary lithium silicide Li2IrSi3. The crystal structure of Li2IrSi3 consists of IrSi6 antiprisms connected by Si triangles, giving rise to a three dimensional framework of covalent Si-Si and Si-Ir bonds. The electronic specific heat in the superconducting phase suggests that Li2IrSi3 is a BCS weak-coupling superconductor.

    DOI: 10.7566/JPSJ.83.103703

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    arXiv

  71. Spin and Orbital Contributions to Magnetically Ordered Moments in 5d Layered Perovskite Sr2IrO4 Reviewed

    Fujiyama S, Ohsumi H, Ohashi K, Hirai D, Kim B. J, Arima T, Takata M, Takagi H

    PHYSICAL REVIEW LETTERS   Vol. 112 ( 1 ) page: 016405   2014.1

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    The ratio of orbital (L) and spin (S) contributions to the magnetically ordered moments of a 5d transition metal oxide, Sr2IrO4 was evaluated by nonresonant magnetic x-ray diffraction. We applied an improved experimental setting that minimized the experimental error, in which we varied only the linear polarization of incident x ray at a fixed scattering angle. Strong polarization dependence of the intensity of magnetic diffraction was observed, from which we conclude that the ordered moments contain substantial contribution from the orbital degree of freedom with the ratio of YLY/YSY∼5.0, evidencing the pronounced effect of spin-orbit coupling. The obtained ratio is close to, but slightly larger than the expected value for the ideal Jeff=1/2 moment of a spin-orbital Mott insulator, |YJ1/2|Lz|J1/2Y|/|YJ1/2|Sz|J1/2Y|=4, which cannot be accounted for by the redistribution of orbital components within the t2g bands associated with the elongation of the IrO6 octahedra. © 2014 American Physical Society.

    DOI: 10.1103/PhysRevLett.112.016405

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  72. Strong Electron-Phonon Coupling Superconductivity Induced by a Low-Lying Phonon in IrGe Reviewed

    Daigorou Hirai, Mazhar N. Ali, Robert J. Cava

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   Vol. 82 ( 12 )   2013.12

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    The physical properties of the previously reported superconductor IrGe and the Rh1-xIrxGe solid solution are investigated. IrGe has an exceptionally high superconducting transition temperature (T-c = 4.7 K) among the isostructural 1 : 1 late-metal germanides MGe (M = Rh, Pd, Ir, and Pt). Specific-heat measurements reveal that IrGe has an anomalously low Debye temperature, originating from a low-lying phonon, compared to the other MGe phases. A large jump at T-c in the specific-heat data clearly indicates that IrGe is a strong coupling superconductor. In the Rh1-xIrxGe solid solution, a relationship between an anomalous change in lattice constants and the Debye temperature is observed. We conclude that the unusually high T-c for IrGe is likely due to strong electron-phonon coupling derived from the presence of a low-lying phonon.

    DOI: 10.7566/JPSJ.82.124701

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  73. Superconducting phase diagram of InxWO3 synthesized by indium deintercalation Reviewed

    Joshua D. Bocarsly, Daigorou Hirai, M. N. Ali, R. J. Cava

    EPL   Vol. 103 ( 1 )   2013.7

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    We report the superconducting phase diagram of the hexagonal tungsten bronze (HTB) InxWO3. The InxWO3 samples were prepared by indium deintercalation of the thermodynamically stable parent phase In0.33WO3. By employing this technique, a lowest indium content in the HTB phase of x similar to 0.07 was achieved, which cannot be obtained by conventional solid-state reaction. In addition, accurately and reproducibly controlled indium content and homogeneous samples enable us to perform a systematic study of the physical properties of InxWO3. Most of the InxWO3 samples exhibit a superconducting transition and the highest transition temperature T-c = 4.2 K in InxWO3 was observed at x = 0.11. The indium content dependence of T-c(x) shows remarkable similarities to other MxWO3 (M = K and Rb) HTBs. Our results reveal the universality of physical properties in the HTB family and give a strategy to achieve higher T-c in HTBs. Copyright (c) EPLA, 2013

    DOI: 10.1209/0295-5075/103/17001

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  74. Superconductivity in the Cu(Ir1-xPtx)(2)Se-4 spinel Reviewed

    Huixia Luo, Tomasz Klimczuk, Lukas Muechler, Leslie Schoop, Daigorou Hirai, M. K. Fuccillo, C. Felser, R. J. Cava

    PHYSICAL REVIEW B   Vol. 87 ( 21 )   2013.6

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    We report the observation of superconductivity in the CuIr2Se4 spinel induced by partial substitution of Pt for Ir. The optimal doping level for superconductivity in Cu(Ir1-xPtx)(2)Se-4 is x = 0.2, where T-c is 1.76 K. A superconducting T-c vs composition dome is established between the metallic, normal conductor CuIr2Se4 and semiconducting CuIrPtSe4. Electronic structure calculations show that the optimal T-c occurs near the electron count of a large peak in the calculated electronic density of states and that CuIrPtSe4 is a band-filled insulator. Characterization of the superconducting state in this heavy metal spinel through determination of Delta C/gamma T-c indicates that it is BCS-like. The relatively high upper critical field at the optimal superconducting composition [H-c2(0) = 3.2 T] is much larger than that reported for analogous rhodium spinels and is comparable to or exceeds the Pauli field (mu H-0(P)), suggesting that strong spin-orbit coupling may influence the superconducting state. Further, comparison to doped CuIr2S4 suggests that superconductivity in iridium spinels is not necessarily associated with the destabilization of a charge-ordered spin-paired state through doping.

    DOI: 10.1103/PhysRevB.87.214510

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  75. Synthesis and characterization of two crystallographic forms of Ag0.79VS2 Reviewed

    Mazhar N. Ali, Huiwen Ji, Daigorou Hirai, M. K. Fuccillo, R. J. Cava

    JOURNAL OF SOLID STATE CHEMISTRY   Vol. 202   page: 77 - 84   2013.6

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    A previously unreported compound, Ag0.79VS2, has been synthesized; its structure and elementary properties are reported. Ag0.79VS2 crystallizes in two forms, designated as the alpha and beta, related to the 1s-InTaS2 structure. Single crystal x-ray diffraction shows the alpha form to have a single layer hexagonal structure with a unit cell of 3.213(3) angstrom x 7.809(6) angstrom, consisting of layers of edge-shared VS6 triangular prisms separated by layers of Ag. The beta form is similar but has an a(o)root(3) supercell in the basal plane, yielding a unit cell of 5.573(5) angstrom x 7.822(6) angstrom. Both forms have disordered and displaced silver in the basal plane, but the beta form has partial ordering of its silver sublattice and in-plane vanadium trimers. Resistivity measurements show metallic temperature dependence with an unusual hysteresis between 210 K and 130 K. Magnetic susceptibility measurements show Pauli Paramagnetic behavior. The Seebeck coefficient at 300 K is 42 mu V/K. (C) 2013 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jssc.2013.03.038

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  76. Spontaneous Formation of Zigzag Chains at the Metal-Insulator Transition in the beta-Pyrochlore CsW2O6 Reviewed International coauthorship International journal

    Daigorou Hirai, Martin Bremholm, Jared M. Allred, Jason Krizan, Leslie M. Schoop, Qing Huang, Jing Tao, R. J. Cava

    PHYSICAL REVIEW LETTERS   Vol. 110 ( 16 )   2013.4

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    A paramagnetic metal to nonmagnetic insulator transition at T-MIT = 210 K is reported for the beta-pyrochlore oxide CsW2O6, accompanied by a first order structural transition that creates &lt; 110 &gt; oriented chains in the pyrochlore lattice. Comparison of CsW2O6, which has 1 electron per 2 W sites, to the fully d(0) analog CsTaWO6 shows that the transitions are electronically driven. Corefinement of high resolution synchrotron x-ray and neutron diffraction data shows that the structural distortion that creates the W chains cannot be attributed to simple charge or orbital ordering. Density functional theory calculations suggest that the phase transition is driven by a sharply peaked electronic density of states near the Fermi energy in the cubic beta-pyrochlore phase. A further electronic instability is required to create the insulating ground state. DOI: 10.1103/PhysRevLett.110.166402

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  77. beta-HfCuGe-A new polymorph of HfCuGe with a novel structure type Reviewed

    Leslie M. Schoop, Jared M. Allred, Ni Ni, D. Hirai, Julia Krez, Michael Schwall, Huiwen Ji, Mazhar N. Ali, R. J. Cava

    JOURNAL OF SOLID STATE CHEMISTRY   Vol. 199   page: 66 - 70   2013.3

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    The structure and elementary physical properties of a new intermetallic compound, beta-HfCuGe, are reported. beta-HfCuGe has a tetragonal structure (space group I4/mmm) with lattice constants of a=3.7634(11)angstrom and c=13.499(4) angstrom. The structure, which consists of double layers of Hf stacked with edge-sharing CuGe4 squares, is not typical for intermetallic compounds and appears to be a new structure type. The compound is a weak paramagnet and a normal metal down to 0.4 K. (C) 2012 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jssc.2012.11.001

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  78. Superconductivity in HfCuGe2: A non-magnetic analog of the 1111 iron pnictides Reviewed

    Leslie Schoop, Daigorou Hirai, Claudia Felser, R. J. Cava

    EPL   Vol. 101 ( 6 )   2013.3

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    Bulk superconductivity with a transition temperature T-c = 0.6 K is reported for the intermetallic compound HfCuGe2. HfCuGe2 is structurally related to the "1111" iron pnictide structure, which hosts a large number of Fe-based superconductors. It can therefore be viewed as a non-magnetic analog to the "1111"-type Fe-based superconductors. Copyright (C) EPLA, 2013

    DOI: 10.1209/0295-5075/101/67001

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  79. Superconductivity of BaPbO_3/BaBiO_3 superlattices Reviewed

    Kawasoko H., Matsuno J., Hirai D., Takagi H.

    Meeting Abstracts of the Physical Society of Japan   Vol. 68.2.3 ( 0 ) page: 440   2013

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Physical Society of Japan  

    DOI: 10.11316/jpsgaiyo.68.2.3.0_440_1

    CiNii Research

  80. Synthesis, Structure, and Magnetic Studies of Manganese-Oxygen Clusters of Reduced Coordination Number, Featuring an Unchelated, 5-Coordinate Octanuclear Manganese Cluster with Water-Derived Oxo Ligands Reviewed

    Sandeep K. Kondaveeti, Shivaiah Vaddypally, Carol Lam, Daigorou Hirai, Ni Ni, Robert J. Cava, Michael J. Zdilla

    INORGANIC CHEMISTRY   Vol. 51 ( 19 ) page: 10095 - 10104   2012.10

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

    The synthesis of reduced coordination (less than 6), unchelated manganese oxygen cluster systems is described. Addition of phenols to Mn(NR2)(2) (R = SiMe3) results in protolytic amide ligand replacement, and represents the primary entry into the described chemistry. Addition of PhOH to Mn(NR2)(2) results in the formation of the heteroleptic dimer Mn-2(mu-OPh)(2)(NR2)(2)(THF)(2) (1). Usage of the sterically larger 2,6-diphenylphenol (Ph2C6H3OH) as the ligand source results in the formation of a 3-coordinate heteroleptic dimer without THF coordination, Mn-2(mu-OC6H3Ph2)(2)(NR2)(2) (2). Attempts to generate 2 in the presence of THF or Et2O resulted in isolation of monomeric Mn(OC6H3Ph2)(2)L-2 (3, L = THF, Et2O). Use of the sterically intermediate 2,4,6-trimethylphenol (MesOH) resulted in formation of the linear trinuclear cluster Mn-3(mu-OMes)(4)(NR2)(2)(THF)(2) (4). Reaction of Mn(NR2)(2) with PhOH in the presence of water, or reaction of 1 with water, results in the formation of a 5-coordinate, unchelated Mn-O cluster, Mn-8(mu(5)-O)(2)(mu-OPh)(12)(THF)(6) (5). Preparation, structures, steric properties, and magnetic properties are presented. Notably, complex 5 exhibits a temperature-dependent phase transition between a 4-spin paramagnetic system at low temperature, and an 8-spin paramagnetic system at room temperature.

    DOI: 10.1021/ic202448c

    Web of Science

    PubMed

  81. Emergence of superconductivity in BaNi2(Ge1-xPx)(2) at a structural instability Reviewed International coauthorship International journal

    Daigorou Hirai, F. von Rohr, R. J. Cava

    PHYSICAL REVIEW B   Vol. 86 ( 10 )   2012.9

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    The physical properties and structural evolution of the 122-type solid solution BaNi2(Ge1-xPx)(2) are reported. The in-plane X-X (X = Ge1-xPx) dimer formation present in the end member BaNi2Ge2, which results in a structural transition to orthorhombic symmetry, is completely suppressed to zero temperature on P substitution near x = 0.7, and a dome-shaped superconducting phase with a maximum T-c = 2.9 K emerges. Clear indications of phonon softening and enhanced electron-phonon coupling are observed at the composition of the structural instability. Our findings show that dimer breaking offers possibilities as a tuning parameter of superconductivity.

    DOI: 10.1103/PhysRevB.86.100505

    Web of Science

  82. Strong Coupling Superconductivity at 8.4 K in an Antiperovskite Phosphide SrPt3P

    T. Takayama, K. Kuwano, D. Hirai, Y. Katsura, A. Yamamoto, H. Takagi

    PHYSICAL REVIEW LETTERS   Vol. 108 ( 23 ) page: 237001   2012.6

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    We report the discovery of a family of ternary platinum phosphides APt(3)P (A = Ca, Sr, and La), which crystallize in an antiperovskite-based structure closely related to that of the heavy fermion superconductor CePt3Si. All three phosphides showed superconductivity at low temperatures and the highest critical temperature T-C = 8.4 K was observed for SrPt3P. The analysis of specific heat C(T) for SrPt3P shows clear evidence for very strong coupling s-wave superconductivity with a large ratio between superconducting gap Delta(0) and T-C, 2 Delta(0)/k(B)T(C) similar to 5, and the presence of low-energy phonons. The presence of multiple Fermi surface pockets was inferred from the nonlinear magnetic field dependence of Hall resistivity, which we argue might play a role in realizing the strong coupling of charge carriers with the low-lying phonons.

    DOI: 10.1103/PhysRevLett.108.237001

    Web of Science

    Scopus

    PubMed

  83. Metal-insulator transition and superconductivity induced by Rh doping in the binary pnictides RuPn (Pn=P, As, Sb) Reviewed

    Daigorou Hirai, Tomohiro Takayama, Daisuke Hashizume, Hidenori Takagi

    Physical Review B - Condensed Matter and Materials Physics   Vol. 85 ( 14 )   2012.4

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    Binary ruthenium pnictides, RuP and RuAs, with an orthorhombic MnP structure, were found to show a metal to a nonmagnetic insulator transition at T MI = 270 and 200 K, respectively. In the metallic region above T MI, a structural phase transition, accompanied with a weak anomaly in the resistivity and the magnetic susceptibility, indicative of a pseudogap formation, was identified at T s = 330 and 280 K, respectively. These two transitions were suppressed by substituting Ru with Rh. We found superconductivity with a maximum T c = 3.7 and 1.8 K in a narrow composition range around the critical point for the pseudogap phase, Rh content x c = 0.45 and 0.25 for Ru 1-xRh xP and Ru 1-xRh xAs, respectively, which may provide us with a nonmagnetic route to superconductivity at a quantum critical point. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.85.140509

    Web of Science

    Scopus

  84. Low temperature synthesis of <i>Ln</i>OF rare-earth oxyfluorides through reaction of the oxides with PTFE Reviewed

    Dutton, SE; Hirai, D; Cava, RJ

    MATERIALS RESEARCH BULLETIN   Vol. 47 ( 3 ) page: 714 - 718   2012.3

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    DOI: 10.1016/j.materresbull.2011.12.014

    Web of Science

  85. Destabilization of the 6H-SrIrO<sub>3</sub> polymorph through partial substitution of zinc and lithium Reviewed

    Bremholm, M; Yim, CK; Hirai, D; Climent-Pascual, E; Xu, Q; Zandbergen, HW; Ali, MN; Cava, RJ

    JOURNAL OF MATERIALS CHEMISTRY   Vol. 22 ( 32 ) page: 16431 - 16436   2012

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    DOI: 10.1039/c2jm32558f

    Web of Science

  86. Superconductivity in WO<sub>2.6</sub>F<sub>0.4</sub> synthesized by reaction of WO<sub>3</sub> with teflon Reviewed

    Hirai, D; Climent-Pascual, E; Cava, RJ

    PHYSICAL REVIEW B   Vol. 84 ( 17 )   2011.11

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    DOI: 10.1103/PhysRevB.84.174519

    Web of Science

  87. 25pTB-6 Effects of defects on AC response of metallic carbon nanotubes Reviewed

    Hirai D., Yamamoto T., Watanabe S.

    Meeting Abstracts of the Physical Society of Japan   Vol. 66.1.4 ( 0 ) page: 853   2011

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    DOI: 10.11316/jpsgaiyo.66.1.4.0_853_1

    CiNii Research

  88. 26pEC-10 Measurements of electrical resistivity on CeRu_2Al_<10> under pressure II Reviewed

    Kawamura Y., Hirai D., Nishioka T., Kato H., Matsumura M., Matsubayashi K., Uwatoko Y.

    Meeting Abstracts of the Physical Society of Japan   Vol. 66.1.3 ( 0 ) page: 599   2011

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    DOI: 10.11316/jpsgaiyo.66.1.3.0_599_1

    CiNii Research

  89. Superconductivity in 4d and 5d transition metal layered pnictides BaRh2P2, BaIr2P2 and SrIr2As2 Reviewed

    Hirai D, Takayama T, Hashizume D, Higashinaka R, Yamamoto A, Hiroko A. K, Takagi H

    Physica C-Superconductivity and Its Applications   Vol. 470 ( SUPPL.1 ) page: S296 - S297   2010.12

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    DOI: 10.1016/j.physc.2009.11.059

    Web of Science

    Scopus

  90. 20aGE-1 Superconductivity in novel platinum pnictidesDepartment of Advanced Materials, University of Tokyo Reviewed

    Kuwano K., Hirai D., Takayama T., Katsura Y., Hashizume D., Yamamoto A., Takagi H.

    Meeting Abstracts of the Physical Society of Japan   Vol. 65.1.3 ( 0 ) page: 528   2010

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:The Physical Society of Japan  

    DOI: 10.11316/jpsgaiyo.65.1.3.0_528_3

    CiNii Research

  91. Superconductivity in Layered Pnictides BaRh<SUB>2</SUB>P<SUB>2</SUB> and BaIr<SUB>2</SUB>P<SUB>2</SUB> Reviewed

    Hirai Daigorou, Takayama Tomohiro, Higashinaka Ryuji, Aruga-Katori Hiroko, Takagi Hidenori

    Journal of the Physical Society of Japan   Vol. 78 ( 2 ) page: 023706 - 023706   2009.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:THE PHYSICAL SOCIETY OF JAPAN  

    Bulk superconductivity was discovered in BaRh<SUB>2</SUB>P<SUB>2</SUB> (<I>T</I><SUB>c</SUB>=1.0 K) and BaIr<SUB>2</SUB>P<SUB>2</SUB> (<I>T</I><SUB>c</SUB>=2.1 K), which are isostructural to (Ba,K)Fe<SUB>2</SUB>As<SUB>2</SUB>, indicative of the appearance of superconductivity over a wide variety of layered transition metal pnictides. The electronic specific heat coefficient γ in the normal state, 9.75 and 6.86 mJ/(mol K<SUP>2</SUP>) for BaRh<SUB>2</SUB>P<SUB>2</SUB> and BaIr<SUB>2</SUB>P<SUB>2</SUB> respectively, indicate that the electronic density of states of these two compounds are moderately large but smaller than those of Fe pnictide superconductors. The Wilson ration <I>R</I><SUB>W</SUB>=χ⁄γ×π<SUP>2</SUP> <I>k</I><SUB>B</SUB><SUP>2</SUP>⁄3μ<SUB>B</SUB><SUP>2</SUP> close to 1 indeed implies the absence of strong electron correlations and magnetic fluctuations unlike Fe pnictides.

    DOI: 10.1143/JPSJ.78.023706

    Web of Science

    Scopus

    CiNii Research

  92. Is there 1/8-anomaly of <i>T</i><sub>c</sub> in Ca<sub>2-<i>x</i></sub>Na<i><sub>x</sub></i>CuO<sub>2</sub>Cl<sub>2</sub> with a checkerboard-type charge ordering? Reviewed

    Hirai, D; Sasagawa, T; Takagi, H

    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   Vol. 463 ( SUPPL. ) page: 56 - 59   2007.10

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    Motivated by the recent discovery of a "checkerboard"-type charge ordering in Ca2 s(-) xNaxCuO2Cl2 high-Tc superconductors, the doping dependence of Tc has been carefully examined in this compound to clarify whether there is any anomaly in the phase diagram, which has been observed at 1/8-doping in the isostructural La2CuO4-based superconductors with a different "stripe"-type ordering. It is shown that the improved sample preparation can increase the maximum Tc by 3 K, and that there is not any anomalous suppression of Tc at any specific doping in Ca2 s(-) xNaxCuO2Cl2. Taking into account the recent STM/STS observations of the checkerboard charge ordering, its impact on superconductivity is discussed. © 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physc.2007.01.034

    Web of Science

    Scopus

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MISC 25

  1. Kitaevスピン液体候補物質OsCl<sub>3</sub>の合成と物性

    片岡亨太, 平井大悟郎, 矢島健, 浜根大輔, 橘高俊一郎, 榊原俊郎, 広井善二

    日本物理学会講演概要集(CD-ROM)   Vol. 74 ( 1 )   2019

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  2. Strong Electron-Phonon Coupling Superconductivity Induced by a Low-lying Phonon in IrGe

    Daigorou Hirai, Mazhar. N. Ali, R. J. Cava

    J. Phys. Soc. Jpn. 82, 124701 (2013)     2018.3

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    Publishing type:Internal/External technical report, pre-print, etc.  

    The physical properties of the previously reported superconductor IrGe and<br />
    the Rh1-xIrxGe solid solution are investigated. IrGe has an exceptionally high<br />
    superconducting transition temperature (Tc = 4.7 K) among the isostructural 1:1<br />
    late-metal germanides MGe (M = Rh, Pd, Ir and Pt). Specific-heat measurements<br />
    reveal that IrGe has an anomalously low Debye temperature, originating from a<br />
    low-lying phonon, compared to the other MGe phases. A large jump at Tc in the<br />
    specific-heat data clearly indicates that IrGe is a strong coupling<br />
    superconductor. In the Rh1-xIrxGe solid solution, a relationship between an<br />
    anomalous change in lattice constants and the Debye temperature is observed. We<br />
    conclude that the unusually high Tc for IrGe is likely due to strong<br />
    electron-phonon coupling derived from the presence of a low-lying phonon.

    DOI: 10.7566/JPSJ.82.124701

    arXiv

  3. パイロクロア酸化物超伝導体Cd<sub>2</sub>Re<sub>2</sub>O<sub>7</sub>の純良単結晶育成と正方晶ドメイン構造

    松林康仁, 平井大悟郎, 浜根大輔, 徳永将史, 広井善二

    日本物理学会講演概要集(CD-ROM)   Vol. 73 ( 1 )   2018

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  4. <sup>31</sup>P NMR study on RuP single crystal

    Li Shang, Kobayashi Y, Itoh M, Hirai D, Hiroi Z, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 72 ( 0 ) page: 2269 - 2269   2017

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    &lt;p&gt;RuPの多結晶では、270K以下で非磁性絶縁体相、330K以上で金属相をとり、中間の温度域では擬ギャップ的な振る舞いを示す相が存在することが報告されてきた。この系に、Rhをドープすることで非磁性絶縁転移がx∼0.05で消失し、さらに、擬ギャップ転移がなくなるx∼0.45で超伝導転移温度Tcが最大となる超伝導相が出現することで注目されてきた。しかしながら、単結晶の母物質のRuPは、270K以下が金属的な振る舞いをしている。我々は、単結晶の^31^P核のNMR測定を行い、NMRから見た違いを検討していきたい。&lt;/p&gt;

  5. Material development and magnetism in metal carbodiimide compounds

    Tanaka Hidetake, Hirai Daigorou, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 72 ( 0 ) page: 2221 - 2221   2017

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    &lt;p&gt;NCN分子を持つカルボジイミド化合物では、直線状のNCN分子が2価のアニオンとして振る舞い、磁性金属イオンと結合して様々な結晶格子を組む。例えば、MnNCNは岩塩構造をもつMnOを111方向に伸ばした構造を持つ。われわれは、3d電子系と4f電子系の両面から物質探索を行い、基礎物性を測定している。発表では、合成した物質に対し類似構造を持つ酸化物や他のイオン化合物と比較を通して、金属カルボジイミド化合物の磁性を明らかにする。&lt;/p&gt;

  6. 22aBD-5 Exploration of multipole order in Re double perovskite

    Hirai D, Yajima T, Hiroi Z

    Meeting Abstracts of the Physical Society of Japan   Vol. 71 ( 0 ) page: 2344 - 2344   2016

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    DOI: 10.11316/jpsgaiyo.71.1.0_2344

    CiNii Books

  7. Pleochroism as a manifestation of 5d orbital state

    Hirai Daigorou, Yajima Takeshi, Kim Changsu, Akiyama Hidefumi, Hiroi Zenji

    Meeting Abstracts of the Physical Society of Japan   Vol. 71 ( 0 ) page: 1802 - 1802   2016

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    &lt;p&gt;多色性とは結晶の色が偏光面と結晶軸、観察方向の位置関係によって異なる色に見える光学現象である。本研究では、新たに合成されたレニウムの酸塩化物の多色性について報告する。この化合物は結晶のa軸方向から見ると茶色に、a軸と垂直方向から見ると緑色に見える。発表では、測定された吸収スペクトルをレニウムの5d軌道状態から議論する。&lt;/p&gt;

    DOI: 10.11316/jpsgaiyo.71.2.0_1802

  8. Investigation on novel physical properties in 5d pyrochlore oxides

    Matsubayashi Y, Hirai D, Hiroi Z

    Meeting Abstracts of the Physical Society of Japan   Vol. 71 ( 0 ) page: 2246 - 2246   2016

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    &lt;p&gt;スピン軌道相互作用(SOC)が強く働く4d、5d遷移金属化合物では、SOCが電子間のクーロン反発と競合し、3d遷移金属化合物では現れない電子相の発現が期待されている。本研究室では、Cd_2_Re_2_O_7_の超伝導やCd_2_Os_2_O_7_のAll-in All-out磁気秩序など5d遷移金属パイロクロア酸化物の新奇物性を示してきた。本発表では、5d遷移金属元素を含むパイロクロア酸化物Cd_2_Re_2_O_7_、Cd_2_Ir_2_O_7_における新奇物性探索について述べる。&lt;/p&gt;

    DOI: 10.11316/jpsgaiyo.71.2.0_2246

  9. 22aBC-13 Metal-insulator transition induced by magnetic impurity in SrIrO_3

    Matsui N, Shintani D, Hirai D, Nonaka Y, Shibata G, Fujimori A, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 70 ( 0 ) page: 2079 - 2079   2015

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    DOI: 10.11316/jpsgaiyo.70.1.0_2079

    CiNii Books

  10. 8pBK-2 Transport properties of Heavy Fermions in LiV_2O_4 thin films

    Niemann U., Hirai D., Takagi H.

    Meeting abstracts of the Physical Society of Japan   Vol. 69 ( 2 ) page: 393 - 393   2014.8

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    CiNii Books

  11. 27aCE-10 NMR Study on Pseudo Gap of Ru_<1-x>Rh_xP

    Li S, Kobayashi Y, Itoh M, Hirai D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 69 ( 0 ) page: 545 - 545   2014

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    CiNii Books

  12. 9aPS-129 ^<31>P NMR Study on the Electronic States of Ru_<1-x>Rh_xP

    Li S, Kobayashi Y, Itoh M, Hirai D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 69 ( 0 ) page: 432 - 432   2014

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    CiNii Books

  13. 8pBJ-9 Spin-orbit Coupling Induced Semimetal in Perovskite CaIrO_3

    Hirai D, Matsuno J, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 69 ( 0 ) page: 391 - 391   2014

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    CiNii Books

  14. Superconductivity of BaPbO_3/BaBiO_3 superlattices

    Kawasoko H, Matsuno J, Hirai D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 68 ( 0 ) page: 440 - 440   2013

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    CiNii Books

  15. Zigzag Chain Formation at a Metal-Insulator Transition in CsW_2O_6

    Hirai D, Breholm M, Allred M.J, Krizan J, Schoop M.L, Huang Q, Tao J, Cava J.R

    Meeting Abstracts of the Physical Society of Japan   Vol. 68 ( 0 ) page: 584 - 584   2013

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    CiNii Books

  16. 24pGE-9 Photoemission study of RuP

    Sato K, Wakisaka Y, Mizokawa T, Arita S, Namatame H, Taniguchi M, Hirai D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 66 ( 0 ) page: 654 - 654   2011

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    CiNii Books

  17. 20aGE-1 Superconductivity in novel platinum pnictidesDepartment of Advanced Materials, University of Tokyo

    Kuwano K, Hirai D, Takayama T, Katsura Y, Hashizume D, Yamamoto A, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 65 ( 0 ) page: 528 - 528   2010

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    Language:Japanese   Publisher:The Physical Society of Japan  

    CiNii Books

  18. 24aWB-5 Superconductivity and competing order in RuX (X=As,P)

    Hirai D, Takayama T, Yamamoto A, Hashizume D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 65 ( 0 ) page: 541 - 541   2010

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    CiNii Books

  19. 23pGE-4 Superconductivity at Quantum Critical Point in RuAs

    Hirai D, Takayama T, Yamamoto A, Hashizume D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 65 ( 0 ) page: 682 - 682   2010

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    CiNii Books

  20. 26aPS-134 Physical properties of ATMBi_2 compounds with Iron-pnictide related structure

    Hirai D, Takayama T, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 64 ( 0 ) page: 507 - 507   2009

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    CiNii Books

  21. 27pTC-15 Superconductivity in layered pnictides with 4,5d transition metals

    Hirai D, Takayama T, Yamamoto A, Hashizume D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 64 ( 0 ) page: 558 - 558   2009

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    Language:Japanese   Publisher:The Physical Society of Japan  

    DOI: 10.1143/JPSJ.78.023706

    CiNii Books

  22. 20aYA-9 Superconductivity in oxypnictide NdFePO

    Hirai D, Kuwano K, Takayama T, Nohara M, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 63 ( 0 ) page: 447 - 447   2008

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    CiNii Books

  23. 26pYB-9 Magnetic and Transport Properties of Calcium-ferrite type Oxide NaV_2O_4

    Hirai D, Takayama T, Yamamoto A, Hashizume D, Pchelkina Zlata, Arita R, Matsuda M, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 63 ( 0 )   2008

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    J-GLOBAL

  24. 20pWG-5 High Pressure Synthesis and Physical Property of Novel Mix Valence Oxide NaV_2O_4

    Hirai D, Takayama T, Yamamoto A, Hashizume D, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 62 ( 0 ) page: 626 - 626   2007

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    CiNii Books

  25. 24pWH-5 High Pressure Synthesis of New Layered Nickel Oxychlorides Sr_2NiO_<2+x>Cl_<2-x>

    Hirai D, Sasagawa T, Takayama T, Takagi H

    Meeting Abstracts of the Physical Society of Japan   Vol. 62 ( 0 ) page: 663 - 663   2007

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Presentations 1

  1. One-dimensionalization by frustration in the anisotropic triangular lattice of the 5d quantum antiferromagnets A3ReO5Cl2 (A = Ca, Sr, and Ba) International conference

    Daigorou Hirai, K. Nawa, T. Yajima, M. Kawamura, T. Misawa, Z. Hiroi

    International Conference on Highly Frusturated Magnetism 2018  2018.7.13 

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    Language:English   Presentation type:Poster presentation  

KAKENHI (Grants-in-Aid for Scientific Research) 9

  1. 1000 T結晶格子の探索と解明

    Grant number:23H04860  2023.4 - 2028.3

    科学研究費助成事業  学術変革領域研究(A)

    大和田 謙二, 松田 康弘, 加藤 大地, 平井 大悟郎, 塚田 真也

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    Authorship:Coinvestigator(s) 

    化学結合の視点に立ち、超強磁場中で発現する新たな固体結晶の探索・解明を戦略的に行う。共有結合やイオン結合、水素結合の観点から化学結合への磁場効果を捉え、より微視的な分子軌道描像・電子分布から理解することで、化学結合への非摂動磁場効果を量子力学的に解明する。これまで磁場効果の研究対象とはならなかったBaTiO3やPbTiO3などの強誘電体、VO2などの分子軌道結晶をはじめとした量体化物質、水素結合が重要となる鉱物結晶であるボルボサイトやKDPなどの誘電体について、1000 テスラ超強磁場中での結晶構造相転移の探索を、電気的、磁気的、光学的(X線を含む)測定から明らかにする。

  2. Elucidation of volumetric function mechanism in pyrovanadate Cu2V2O7

    Grant number:23H01837  2023.4 - 2026.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

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    Authorship:Coinvestigator(s) 

  3. Material search and investigation of spin-nematic state induced by spin-orbit interaction

    Grant number:22H04462  2022.4 - 2024.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\5850000 ( Direct Cost: \4500000 、 Indirect Cost:\1350000 )

  4. Material research and physics of multipole in 5d electron systems

    Grant number:20H01858  2020.4 - 2024.3

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

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\17680000 ( Direct Cost: \13600000 、 Indirect Cost:\4080000 )

  5. New optical and electronic properties designed by coordination engineering

    Grant number:19H04688  2019.4 - 2021.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\5200000 ( Direct Cost: \4000000 、 Indirect Cost:\1200000 )

  6. Material research and physics of multipole in 5d electron systems

    Grant number:18K13491  2018.4 - 2020.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Early-Career Scientists

    Hirai Daigorou

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\4160000 ( Direct Cost: \3200000 、 Indirect Cost:\960000 )

    In 5d transition metal compounds, electrons are expected to acquire multipolar degree of freedom due to the combined effect of electron correlations and strong spin-orbit interactions. In this work, we synthesized a series of double perovskite-type compounds containing 5d transition metal ion with 5d1 electronic configuration, and experimentally revealed spin-orbit entangled electronic state in these compounds by magnetic susceptibility and heat capacity measurements. Then, we grew high-quality single crystals of Ba2MgReO6, which shows successive phase transitions at low temperatures, for detailed measurements. We successfully observed quadrupolar ordering of 5d electrons by synchrotron x-ray diffraction measurements.

  7. Itinerant multipole order in spin-orbit-coupled metals

    Grant number:18H04308  2018.4 - 2020.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\8970000 ( Direct Cost: \6900000 、 Indirect Cost:\2070000 )

  8. New route of anion exchange reactions and physical properties of mixed anion compounds

    Grant number:15K17695  2015.4 - 2017.3

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

    Hirai Daigorou

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

    We aimed at establishing a new route of anion exchange reactions for controlling physical properties of transition metal oxides and exploring novel properties of mixed-anion compounds. By using tetrafluoroethlene (teflon)/melamine as anion sources, we succeeded in performing anion exchange reactions. This method enabled us to synthesize various mixed-anion compounds including a new compound Lu2O2NCN. In addition, we investigated unique properties of mixed anion compounds and discovered a very strong pleochroism in a new mixed anion compound Ca3ReO5Cl2.

  9. 5d遷移金属酸化物におけるスピン軌道相互作用と電子相関の協奏物性の開拓

    Grant number:09J07391  2009 - 2010

    日本学術振興会  科学研究費助成事業  特別研究員奨励費

    平井 大悟郎, 平井 大悟郎

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    Authorship:Other  Grant type:Competitive

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

    本研究では、4d,5d遷移金属を用いて物質を合成することにより、4d,5d電子系の物性を開拓することを目的としている。4d,5d電子系はスピン軌道相互作用・電子相関・結晶場の複合物性が期待できる有望な舞台である。
    1.4d遷移金属ニクタイド RuPとRuAsにおける金属絶縁体転移の発見
    4d遷移金属ニクタイドにおいて、構造相転移を伴う新規金属絶縁体転移を発見した。これまで4d遷移金属ニクタイドは物性研究の対象として注目されてこなかったが、本研究での金属絶縁体転移の発見により、4d遷移金属ニクタイドが多様な物性を示し、物性研究の舞台として有望であることが示された。この金属絶縁体転移は結晶の構造相転移を伴っており、スピン・軌道の自由度が4d,5d電子系においても重要な役割を果たしていることが明らかになった。
    2.新超伝導体Rh置換RuP,RuAs,とRuSb
    上述の金属絶縁体転移を示す4d遷移金属ニクタイドにRhを置換することで、超伝導を発現させることに成功した。超伝導転移温度はそれぞれ、(Ru,Rh)Pで3.7K(Ru,Rh)Asで1.8KさらにRuSbで1.16Kと低いが、相転移の臨界点における超伝導という観点から、非常に興味深い特徴を持つ発見といえる。臨界点における超伝導には、高温超伝導体などが含まれ、学術的にも、実用面からも重要な分野である。特に今回の超伝導は、非磁性絶縁体相の臨界点における超伝導という、これまでに報告のない新たな分野である可能性があり、重要な発見であると考えられる。

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Media Coverage 5

  1. 新しいハイエントロピー型アンチモン化合物で超伝導を観測 Internet

    EE Times Japan  2023.8

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  2. Unveiling the mechanism of the metal-to-insulator transition in ruthenium phosphide suggests a new way of looking at solids Internet

    EurekAlert AAAS  2022.11

  3. The Mechanism of the Metal-to-Insulator Transition in Ruthenium Phosphide Internet

    Lab Manager  2022.11

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  4. 名古屋大学などが無機固体の新結合発見、センサーやスイッチング素子への応用期待 Internet

    日経XTECH  2022.10

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  5. 名大、リン化ルテニウムが0℃付近で金属から絶縁体に変化する理由を解明 Internet

    TECH+ powered by マイナビニュース  2022.9

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    Author:Other