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 Zn₂P₂O₇. Particularly, Zn_1.6Mg_0.4P₂O₇ 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

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

DOI： 10.7566/JPSJ.92.074703

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

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

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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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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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 Ca₃ReO₅Cl₂ 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 Ca₃ReO₅Cl₂, 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

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

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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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_c of 7 K, while the latter does not exhibit superconductivity. We prepared single crystals of solid solution NaAlSi_1–xGe_x 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_c 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_c 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

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

DOI： 10.7566/JPSJ.91.074801

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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

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

<title>Abstract</title>
Semimetallic osmium pyrochlore oxide Cd₂Os₂O₇ 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 Hg₂Os₂O₇ 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 Hg₂Os₂O₇ is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd₂Os₂O₇. Hg₂Os₂O₇ 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.

DOI： 10.1088/1361-648X/ac4936

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/ac4936/pdf

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

DOI： 10.7566/JPSJ.91.024702

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

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

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.

DOI： 10.7566/JPSJ.91.013702

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

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.

DOI： 10.1103/PhysRevB.105.035116

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

DOI： 10.1103/PhysRevB.104.174422

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.104.174422/fulltext

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan  

<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, Ca₃ReO₅Cl₂, 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

CiNii Research

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

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.

DOI： 10.7566/JPSJ.90.094708

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.iecr.1c01424

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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.

DOI： 10.7566/JPSJ.90.064714

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

DOI： 10.1088/1361-648X/abda79

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

DOI： 10.7566/JPSJ.90.034710

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Vacuum and Surface Science  

<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

CiNii Research

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

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.

DOI： 10.7566/JPSJ.89.114711

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

DOI： 10.7566/JPSJ.89.114709

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

DOI： 10.1103/PhysRevResearch.2.043121

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

DOI： 10.1103/PhysRevB.102.155131

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.inorgchem.0c01187

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DOI： 10.1103/PhysRevB.101.220412

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DOI： 10.1103/PhysRevResearch.2.022063

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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.

DOI： 10.1103/PhysRevB.101.205133

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

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.

DOI： 10.7566/JPSJ.89.053701

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

DOI： 10.1103/PhysRevB.101.165113

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.101.165113/fulltext

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

DOI： 10.7567/1347-4065/ab65ab

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.inorgchem.9b01869

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DOI： 10.7566/JPSJ.88.064712

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

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.

DOI： 10.1021/acs.chemmater.9b00420

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Scopus

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

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.

DOI： 10.7566/JPSJ.88.044708

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Scopus

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

DOI： 10.11316/jpsgaiyo.74.2.0_2013

CiNii Research

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

DOI： 10.11316/jpsgaiyo.74.1.0_2382

CiNii Research

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

DOI： 10.11316/jpsgaiyo.74.1.0_2313

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

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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Scopus

arXiv

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

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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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

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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Scopus

arXiv

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

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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Scopus

arXiv

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

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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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

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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Scopus

PubMed

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

DOI： 10.11316/jpsgaiyo.73.2.0_1408

CiNii Research

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

DOI： 10.11316/jpsgaiyo.73.2.0_1405

CiNii Research

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

DOI： 10.11316/jpsgaiyo.73.1.0_2302

CiNii Research

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

DOI： 10.11316/jpsgaiyo.73.1.0_2303

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

DOI： 10.11316/jpsgaiyo.73.1.0_2044

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

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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Scopus

PubMed

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

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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Scopus

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

DOI： 10.11316/jpsgaiyo.72.2.0_1794

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

DOI： 10.11316/jpsgaiyo.72.2.0_1788

CiNii Research

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

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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Scopus

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

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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Scopus

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

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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Scopus

arXiv

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

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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Scopus

PubMed

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

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

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY  

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

Web of Science

Scopus

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

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

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

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

Web of Science

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

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

DOI： 10.1103/PhysRevLett.110.166402

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

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

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY  

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

Web of Science

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

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

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PubMed

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

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

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

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

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Scopus

PubMed

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

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

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Scopus

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

DOI： 10.1016/j.materresbull.2011.12.014

Web of Science

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

DOI： 10.1039/c2jm32558f

Web of Science

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

DOI： 10.1103/PhysRevB.84.174519

Web of Science

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

DOI： 10.11316/jpsgaiyo.66.1.4.0_853_1

CiNii Research

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

DOI： 10.11316/jpsgaiyo.66.1.3.0_599_1

CiNii Research

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

DOI： 10.1016/j.physc.2009.11.059

Web of Science

Scopus

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

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

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physica C: Superconductivity and its Applications  

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

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Scopus

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.1.0_2344

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

&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

Language：Japanese   Publisher：The Physical Society of Japan  

&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

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.70.1.0_2079

CiNii Books

Language：English   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.1143/JPSJ.78.023706

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Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

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Language：Japanese   Publisher：The Physical Society of Japan  

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