記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 粉体粉末冶金協会  

Large negative thermal expansion (NTE) was achieved at room temperature using the structural phase transition in Zn2P2O7. Particularly, Zn1.6Mg0.4P2O7 has a negative coefficient of linear thermal expansion αL 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.

DOI： 10.2497/jjspm.23-00009

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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

In topological materials, peculiar surface states protected by crystal symmetries have attracted great interest because of the possibility of unprecedented correlation with superconductivity. A topological nodal-line semimetal with a layered structure, NaAlSi shows moderately anisotropic bulk superconductivity with Tc ≅ 7.0 K. The magnetic torque curves as a function of the field angle in the superconducting state are found to show two distinct diamagnetic signals; a large broad signal arising from bulk superconductivity and a small sharp signal observed only in magnetic fields nearly parallel to the layers. The upper critical field of the bulk superconductivity follows an anisotropic 3D model with a small anisotropic factor of ∼4. A possible scenario is that the sharp signal is due to highly 2D superconductivity with a similar Tc, whose thickness is only several times of the c-axis lattice constant (0.736 nm). The band structure calculations show the presence of large Fermi lines on the (001) plane, mainly formed by the surface Si p bands. The sharp diamagnetic torque signal could arise from the (001) surface superconductivity.

DOI： 10.7566/JPSJ.92.074703

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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 ΔV/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 ΔV/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 ΔV/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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

The electrical resistivity, magnetic susceptibility, and heat capacity of sintered samples of Ca2Ir2O7, in which pentavalent Ir atoms with 5d 4 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

The observation of spinon excitations in the S=12 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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その他リンク： https://www.nature.com/articles/s41467-022-33992-5

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the American Chemical Society  

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.

DOI： 10.1021/jacs.2c06173

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics: Conference Series  

NaAlSi and NaAlGe are nodal-line semimetals with an anti-PbFCl type structure. The former is a superconductor with a transition temperature Tc of 7 K, while the latter does not exhibit superconductivity. We prepared single crystals of solid solution NaAlSi1-x Ge 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 Tc 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 Tc 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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その他リンク： https://iopscience.iop.org/article/10.1088/1742-6596/2323/1/012004/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

NaAlSi and NaAlGe are isostructural and isoelectronic semimetals with topological nodal lines close to the Fermi level. Despite having virtually identical electronic structures, NaAlSi exhibits superconductivity below Tc = 6.8 K, whereas NaAlGe does not. We investigate NaAlGe by measuring its electrical resistivity, Hall effect, magnetic susceptibility, and heat capacity using single crystals. It is revealed that NaAlGe is not a simple semimetal but rather has an unusual ground state with a small pseudogap of ~100K close to the Fermi level. We argue that the formation of the pseudogap in NaAlGe is due to an unexpected Fermi surface instability, such as an excitonic instability, as opposed to the electron-phonon instability that leads to the formation of the superconducting gap in NaAlSi.

DOI： 10.7566/JPSJ.91.074801

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.105.235103/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

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 5d electrons with moderate electron correlations and strong spin-orbit interactions.

DOI： 10.1088/1361-648X/ac4936

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/ac4936/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

NaAlSi is a quasi-two-dimensional semimetal with superconductivity below Tc = 6.8 K and a band structure characterized by nodal lines near the Fermi level and potential topological surface states. Electrical resistivity measurements on its superconducting transitions in magnetic fields were made using plate-like single crystals. In the magnetic field–temperature phase diagram, we observed a substantial reduction in resistivity in a pre-transitional zone above the bulk superconducting regime only when the magnetic fields were perpendicular to the plane, rather than parallel to it. Significant sample (thickness) dependence, reentrant behavior, and sensitivity to electrode configurations all indicate that a portion of the crystal has an upper critical field greater than the bulk superconductivity in the pre-transitional region. This fractional superconductivity may occur on the side surface of the crystal.

DOI： 10.7566/JPSJ.91.024702

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

Substitution effects of Os for Ru in α-RuCl3 are investigated in a wide composition range of 0 ≤ x ≤ 0.67 in Ru1-x-OsxCl3by 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 130K for 0.15 ≤ x ≤ 0.40, and a magnetic short-range order for x > 0.40. A dimerization as similarly observed in α-RuCl3under 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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 3z2-r2-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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

Magnetic properties of an antiferromagnetic double perovskite oxide Ba2CaReO6, where Re6+ (5d1) ions with large spin-orbit coupling are arranged on the face-centered-cubic lattice, are investigated using pulsed high magnetic field up to 66 T. Magnetization and magnetostriction measurements have revealed a magnetic field-induced phase transition at around 50 T. The phase transition accompanies a jump of magnetization and longitudinal magnetostriction of approximately 2×10-4 with the change of power-law behavior, indicating sizable coupling between the electronic degrees of freedom and the lattice. The high-field phase exhibits a magnetic moment approximately 0.2 μB, which is close to the values observed in 5d1 double perovskite oxides with noncollinear magnetic structure. We argue that Ba2CaReO6 is an antiferromagnet that sits close to the phase boundary between the collinear and noncollinear phases, providing the target material for investigating the interplay between spin-orbital entangled electrons and magnetic field.

DOI： 10.1103/PhysRevB.104.174422

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.104.174422/fulltext

担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

<p>物質が色をもつ理由には様々なものがある．例えば，光の波長程度の構造に由来する構造色や伝導電子によってもたらされる金属特有の光沢などがある．なかでも，宝石は様々な色で人類を魅了してきた．しかし実は，宝石として知られる無機結晶の多くは典型元素だけを主成分とし，純粋なものは無色透明である．様々な色は，微量に混じった遷移金属元素によりもたらされている．例えば，無色透明なアルミニウム酸化物のコランダムに，およそ1%以下のクロムが混じると赤い色のルビーとなり，鉄やチタンが混じると青いサファイアとなる．結晶中では遷移金属イオンの<i>d</i>軌道が分裂し，その分裂幅に対応したエネルギーをもつ光，つまり特定の色が吸収される．そして吸収された色の補色が，私たちの見ている宝石の色となる．<i>d</i>軌道の分裂幅や吸収の強さは，遷移金属イオンの周りの陰イオン（アニオン）の配置やその対称性に強く依存する．このため，同じクロムが入っていても，コランダムでは赤色のルビーに，緑柱石では緑色のエメラルドとなる．</p><p>ほとんどの宝石の色は1色だけだが，最近我々が合成した複合アニオン化合物Ca₃ReO₅Cl₂は，ある方向から結晶を見ると茶色であり，それと垂直な方向から見ると緑色に見えるというユニークな光学特性を示す．さらに，入射光の偏光を結晶軸<i>a</i>，<i>b</i>，<i>c</i>と平行にすると，それぞれ緑，赤，黄の3色に変化する．見る方向や入射光の偏光によって色が変化する光学特性は「多色性」とよばれ古くから知られているが，Ca₃ReO₅Cl₂のような劇的な色の変化を示す物質は非常に珍しい．</p><p>Ca₃ReO₅Cl₂の場合も，遷移金属元素であるRe（レニウム）の<i>d</i>軌道の分裂幅に対応した光が吸収され色がつく．特徴的なのは，入射光の偏光状態に応じて吸収される光のエネルギーが変化するという点である．この性質は，レニウムを二種類のアニオン，酸素と塩素が取り囲んでいるために生じることを私たちは明らかにした．</p><p>酸化物のように1種類しかアニオンを含まない物質では，ほとんどの場合<i>d</i>軌道は2つの準位にしか分裂しないので，1つのエネルギーの光しか吸収せず1色となる．Ca₃ReO₅Cl₂では，2種類のアニオンが作る複雑な結晶場によってレニウムの<i>d</i>軌道は5つのばらばらなエネルギー準位に分裂し，様々なエネルギーの光を吸収できるようになる．さらに，<i>d</i>軌道と偏光の対称性の関係によって，光による電子励起が許される軌道が異なるため，光の偏光に応じて色が変わる．Ca₃ReO₅Cl₂の多色性を生む電子状態の特徴は，複数のアニオンが陽イオンに配位する「複合アニオン化合物」では普遍的に見られるものである．</p><p>このように複合アニオン化合物では，1種類しかアニオンを含まない物質では実現が難しい，もしくは不可能な物性を実現できることがある．最近，複合アニオン化合物の物質開発が盛んに行われており，今後，ユニークな電子状態に起因した特異な物性のさらなる発見が期待される．</p>

DOI： 10.11316/butsuri.76.10_658

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Industrial and Engineering Chemistry Research  

In this study, an organic solvent-free process for the rapid fabrication of nickel ferrite anchored on reduced graphene oxide (rGONF) was developed using supercritical water. The rGONF was synthesized from metal nitrates, graphene oxide (GO), and water using a lab-scale batch reactor at 673 K and 30 MPa. The organic solvent was eliminated from the entire process to prevent chemicals from remaining in the as-synthesized magnetic nanosorbents for the sake of future use. Characterization by X-ray powder diffraction, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy has clearly shown the in situ formation of uniform and highly crystalline nickel ferrite nanoparticles on the surface of rGO. Magnetic properties of the as-synthesized rGONF determined using a magnetic property measurement system have shown desirable magnetic features to serve as an adsorbent in practical water-treatment applications. Furthermore, characterization results have implied the completion of the synthetic process within 15 min, extremely faster than the conventional methods. The effects of reaction conditions such as the temperature, reaction time, GO loading, and Ni/Fe molar ratio on anchored NiFe2O4 nanoparticles are also reported herein. The results have suggested that nucleation with a low Ni/Fe molar ratio followed by Ni ion uptake will result in particle growth and crystallization of NiFe2O4 at GO surfaces.

DOI： 10.1021/acs.iecr.1c01424

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics Condensed Matter  

The synthesis and physical properties of the double perovskite (DP) compound Ba2CdReO6 with the 5d1 electronic configuration are reported. Three successive phases originating from a spin–orbit-entangled Jeff = 3/2 state, confirmed by a reduced effective magnetic moment of 0.72 μB, were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure at Ts = 170 K, below which the Jeff = 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two more electronic transitions to a possible quadrupole ordered state at Tq = 25 K and an antiferromagnetic order of dipoles with a ferromagnetic moment of ∼0.2 μB at Tm = 12 K. These properties were compared with those of the DP’s sister compounds Ba2BReO6 (B = Mg, Zn, and Ca) and the chemical trend is discussed in terms of the mean-field theory for spin–orbit-coupled 5d electrons (2010 Chen et al Phys. Rev. B 82 174440). The DP Ba2BReO6 compounds provide a unique opportunity for a systematic investigation of symmetry breaking in the presence of multipolar degrees of freedom.

DOI： 10.1088/1361-648X/abda79

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

NaAlSi is an sp electron superconductor crystallizing in a layered structure of the anti-PbFCl type with a relatively high transition temperature Tc of ~7 K. Recent electronic state calculations revealed the presence of topological nodal lines in the semimetallic band structure, which attracted much attention owing to the superconductivity. However, experimental investigation remained limited because of the lack of single crystals. Here, we successfully prepared single crystals of NaAlSi by a Na-Ga flux method and characterized their superconducting and normal-state properties through electrical resistivity, magnetization, and heat capacity measurements. A sharp superconducting transition with a Tc of 6.8K is clearly observed, and heat capacity data suggest an anisotropic superconducting gap. Surprisingly, despite the sp electron system, the normal state is governed by the electron correlations, which is indicated by a T2 resistivity and a Wilson ratio of 2.0. The origin of the electron correlation may be related to the orthogonal saddle-shaped Fermi surfaces derived from the Si px and py states, which intersect with the light Al s bands to form the nodal lines near the Fermi level. These results strongly suggest that the superconductivity of NaAlSi is not caused by a simple phonon mechanism but involves a certain unconventional aspect, although its relevance to the nodal lines is unclear.

DOI： 10.7566/JPSJ.90.034710

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

<p>伝導帯と価電子帯がブリルアンゾーンの線上で交差するギャップレスな電子系はラインノード半金属と呼ばれ、新たなトポロジカル状態として注目を集めている。近年、NaAlSiはラインノード半金属であり、さらに7 Kと比較的高い温度で超伝導転移を示すことが示された。そこで本講演では、NaAlSiで実現している電子状態を明らかにするため極低温走査トンネル顕微鏡測定を行った結果について報告する。</p>

DOI： 10.14886/jvss.2021.0_1ca06

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of 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 Ts1 of ∼200 K (phase II) and further to another noncentrosymmetric tetragonal structure below Ts2 of ∼120 K (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 Ts2 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 Ts2 and turned over across Ts2: resistivity along the c axis is larger (smaller) than that along the a axis by ∼25% for phase II (III) at around Ts2. 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

An osmium chloride with the chemical formula of OsxCl3 (x = 0.81) was synthesized and its crystal structure and thermodynamic properties were investigated. OsxCl3 crystallizes in a layered CdCl2-type structure with the triangular lattice partially occupied by Os ions on average. However, on microscopic length scales, the triangular lattice is composed of nano-domains with a honeycomb arrangement of Os ions, as observed by electron microscopy and Raman scattering experiments. Magnetization and heat capacity measurements revealed an absence of magnetic long-range order down to 0.08 K, while a broad peak in heat capacity at 0.15K may indicate a short-range order in the local honeycomb lattice. OsxCl3 may exhibit certain aspects of the Kitaev spin liquid that are expected for a perfect honeycomb lattice of osmium trichloride.

DOI： 10.7566/JPSJ.89.114709

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Research  

The spin excitations of the S=1/2 anisotropic triangular antiferromagnet Ca3ReO5Cl2 were investigated by inelastic neutron-scattering experiments. The spin excitation spectrum exhibits sharp dispersive modes in addition to a spinonlike continuum. The sharp modes exhibit large and small dispersions along the intrachain (K) and interchain directions (L), respectively, reflecting a one-dimensional character modified by interchain interactions. The dispersion intensity along the interchain direction is enhanced at the wave vectors around (K, L)=(0.25,±1.0) and (0.75, 0.0) (in reciprocal lattice units, r.l.u.). This enhancement is well explained by the formation of bound spinon pairs. These features are reminiscent of the spin excitations observed in the prototypical compound Cs2CuCl4 [Coldea, Phys. Rev. Lett. 86, 1335 (2001)10.1103/PhysRevLett.86.1335; Phys. Rev. B 68, 134424 (2003)10.1103/PhysRevB.68.134424]. The consistency with the simulated spectrum based on the random-phase approximation is better for Ca3ReO5Cl2 than for Cs2CuCl4, indicating that the spin system in the former remains closer to a Tomonaga-Luttinger liquidlike disordered state. In addition, the low-energy modes exhibit a wave-vector shift along the ±K direction, suggesting that uniform intrachain Dzyaloshinskii-Moriya interactions are more relevant in Ca3ReO5Cl2.

DOI： 10.1103/PhysRevResearch.2.043121

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.2.043121/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

Magnetic torque measurements in the spin-orbit coupled metal Cd2Re2O7 have been performed to investigate unique multipole orders associated with inversion symmetry breaking. The torque curves as a function of field angle are decomposed into two terms, a fourfold symmetry term (τ4â H4), corresponding to an electric quadrupole order, and a twofold symmetry term (τ2â H2), likely corresponding to an electric toroidal quadrupole order at low temperatures. Below 20 K, a strong enhancement of the fourfold symmetry term following a large phase change is observed toward the superconducting transition whereas no such behavior is evident in the twofold symmetry term. The results show anomalous changes of the electric quadrupole order at the low temperatures.

DOI： 10.1103/PhysRevB.102.155131

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Solid State Chemistry  

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+ (5d2) 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 Ts1 ​= ​265 ​K and Ts2 ​= ​123 ​K. At Ts1, the magnetic susceptibility is enormously reduced and a structural transition to a monoclinic structure takes place, while relatively small changes are observed at Ts2. 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Inorganic Chemistry  

We report the synthesis, crystal structure, and magnetic properties of the two new quantum antiferromagnets A3ReO5Cl2 (A = Sr, Ba). The crystal structure is isostructural with the mineral pinalite Pb3WO5Cl2, in which the Re6+ ion is square pyramidally coordinated by five oxide atoms and forms an anisotropic triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and J′ in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9) and 9.2 (19.3) K, respectively, with J′/J = 0.47 (0.43) for A = Ba (Sr). For each compound, the heat capacity at low temperatures shows a large T-linear component with no signature of long-range magnetic order above 2 K, which suggests a gapless spin liquid state of one-dimensional character of the J chains in spite of the significantly large J′ couplings. This is a consequence of one-dimensionalization by geometrical frustration in the ATL magnet; a similar phenomenon has been observed in two compounds with slightly smaller J′/J values: Cs2CuCl4 (J′/J = 0.3) and the related compound Ca3ReO5Cl2 (0.32). Our findings demonstrate that 5d mixed-anion compounds provide a unique opportunity to explore novel quantum magnetism.

DOI： 10.1021/acs.inorgchem.0c01187

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

The double-perovskite A2BB′O6 with heavy transition metal ions on the ordered B′ sites is an important family of compounds to study the interplay between electron correlation and spin-orbit coupling. Here we prepared high-quality Sr2MgReO6 powder and single-crystal samples and performed nonresonant and resonant synchrotron X-ray diffraction experiments to investigate its magnetic ground state. By combining the magnetic susceptibility and heat capacity measurements, we conclude that Sr2MgReO6 exhibits a layered antiferromagnetic order at temperatures below ∼55 K with a propagation vector q=(001), which contrasts the previously suspected spin-glass state. Our works clarify the magnetic order in Sr2MgReO6 and demonstrate it as a candidate system to look for magnetic octupolar orders and exotic spin dynamics.

DOI： 10.1103/PhysRevB.101.220412

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Research  

Synchrotron x-ray-diffraction measurements on single crystals of the double perovskite Ba2MgReO6 with 5d1 electronic configurations reveal the successive phase transitions from a disordered state to a quadrupolar order at Tq=33K, and then, to a dipolar ordered state at Tm=18K. The magnetic reflections observed below Tm are indexed to a propagation vector with k=[001], indicating a canted antiferromagnetic order. The very small deformation of ReO6 octahedra observed below Tq demonstrates that the quadrupolar order is composed of antiferroically arranged Qx2-y2 and ferroically arranged Q3z2-r2 moments. These observations are consistent with the mean-field theory for spin-orbit-entangled electrons. Our findings are a significant step towards understanding the intriguing physics of multipoles realized by spin-orbit-entangled 5d electrons.

DOI： 10.1103/PhysRevResearch.2.022063

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

We performed 185=187Re 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 Tc 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=T1, a clear coherence peak was observed just below Tc, 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We investigate the metal to nonmagnetic insulator (MI) transition of MnP-type Ru pnictide RuP using hard x-ray and ultraviolet photoemission spectroscopies. The spectral weight at EF is suppressed below the MI transition temperature TMI, while there is no appreciable change across the pseudogap temperature TPG. The estimated energy scale of the gap is ∼110 meV, which is in good correspondence to the spin gap opening observed in the previous NMR study. According to the band structure calculation, the density of states at EF mainly originates from narrow bands of the Ru 4dxy orbitals. Our results suggest that the fourfold-degenerate Ru 4dxy orbitals are deeply related to the MI transition. Based on the photoemission results and the band structure calculation, we argue the possible origin of the MI transition for polycrystalline RuP.

DOI： 10.1103/PhysRevB.101.165113

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.101.165113/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Rod-shaped single crystals of NaPd3Ge2 with a length of ∼1 mm were grown using the self-flux method. The electrical resistivity exhibits a metal-like temperature dependence with a kink at 115 K, which is due to a structural phase transition not observed in the previous study using polycrystalline samples. The higherature phase of NaPd3Ge2 crystallizes in an orthorhombic structure of the space group Imma, while the lowerature phase is isostructural to NaPd3Si2 (space group: Imm2) as determined by the single-crystal X-ray diffraction analyses at 90 K. The density of states and total energies obtained by the density functional theory calculations reveal that both phases are metallic, and the lowerature structure is more stable.

DOI： 10.7567/1347-4065/ab65ab

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Inorganic Chemistry  

Single crystals of a novel Na-Pt-Si ternary compound, Na3Pt10Si5, were synthesized by heating the constituent elements at 1423 K. It crystallizes in a non-centrosymmetric trigonal structure of space group R32 (Z = 3) with lattice constants of a = 10.1536(3) Å and c = 10.1539(3) Å at 300 K. The structure consists of a three-dimensional framework made of Pt and Si atoms, and the Na atoms are contained in the tunnels of the framework. The large magnitude and the temperature dependence of the atomic displacement parameter of the Na site reveal a large thermal vibration indicative of a "rattling" motion of Na atoms in the oversized tunnel. The electronic structure calculations explain the observed metallic properties on the basis of the covalent bonds between the Pt and Si atoms in the framework and the ionic bonding of the Na atoms to the framework. A type II superconductivity with a transition temperature of 2.9 K and an upper critical field of 2.5 kOe are observed for a polycrystalline sintered bulk sample of Na3Pt10Si5 prepared by heating at 1353 K in Na vapor. Heat capacity measurements reveal a strong coupling superconductivity that is probably caused by an electron-phonon interaction enhanced by the rattling motion of the Na atoms.

DOI： 10.1021/acs.inorgchem.9b01869

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

We report on the cubic double perovskite Ba2MgReO6 containing Re6+ ions with the 5d1 electron configuration. Resistivity, magnetization, and heat capacity measurements using single crystals show that the compound is a Mott insulator with a magnetic transition at Tm = 18 K, which is accompanied by a weak ferromagnetic moment with [110] anisotropy. Another transition is observed at Tq = 33 K in the heat capacity, where the inverse of magnetic susceptibility changes its slope, indicating a substantial change in the electronic state. The significance of spin–orbit coupling is revealed by the reduced effective magnetic moment of ∼0.68μB at high temperatures above Tq and the total electronic entropy close to R ln 4. These features indicate that Ba2MgReO6 is a spin–orbit coupled Mott insulator possessing a Jeff = 3=2 quartet state, which exhibits quadrupolar and dipolar orders at Tq and Tm, respectively.

DOI： 10.7566/JPSJ.88.064712

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the 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 dxy orbital, which are arranged to form a spin-1=2 ATL with J A=J ∼ 0.32 and J = 41 K, where J and J A 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 ATL antiferromagnet, especially via comparison with the typical ATL compound Cs2CuCl4

DOI： 10.7566/JPSJ.88.044708

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.2.0_2013

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.1.0_2382

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.1.0_2313

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

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

DOI： 10.7566/JPSJ.87.104604

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arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition with inversion symmetry breaking (ISB) at Ts1 = 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 5–9m0 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Fluorine Chemistry  

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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arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the 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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of 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 ∼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 lowenergy 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 ∼0.3 eV, which is large enough to be comparable to the valence bandwidth of ∼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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：RSC Advances  

Four anti-perovskite-type compounds, ZnNNi 3 , ZnCNi 3 , SnNCo 3 , and SnCCo 3 , are synthesised through reactions between metal oxides and organic compound melamine (C 3 H 6 N 6 ). ZnNNi 3 and ZnCNi 3 are selectively synthesised by choosing different reaction temperatures and nominal oxide-to-melamine ratios. SnNCo 3 is synthesised for the first time by this melamine method. Resistivity, magnetisation, and heat capacity measurements reveal that SnNCo 3 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

Web of Science

Scopus

PubMed

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_1408

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_2044

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_2303

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_1405

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_2302

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

P31 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 TPG=330K. The first-order MI 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 TMI=270K. In the PG phase of Ru1-xRhxP with 0≤x<0.45, an analysis based on the modified Korringa relation, which is applicable to an itinerant paramagnet with 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∼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

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_1794

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_1788

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

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.

DOI： 10.1063/1.4926723

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：{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.

DOI： 10.1063/1.4913389

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

We report the discovery of superconductivity at Tc = 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

Web of Science

Scopus

arXiv

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/JPSJ.82.124701

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EPL  

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 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 in InxWO 3 was observed at . The indium content dependence of shows remarkable similarities to other MxWO3 ( and Rb) HTBs. Our results reveal the universality of physical properties in the HTB family and give a strategy to achieve higher in HTBs. © Copyright EPLA, 2013.

DOI： 10.1209/0295-5075/103/17001

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.87.214510

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jssc.2013.03.038

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.110.166402

Web of Science

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jssc.2012.11.001

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1209/0295-5075/101/67001

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.2.3.0_440_1

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ic202448c

Web of Science

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.86.100505

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We report the discovery of a family of ternary platinum phosphides APt 3P (A=Ca, Sr, and La), which crystallize in an antiperovskite-based structure closely related to that of the heavy fermion superconductor CePt 3Si. All three phosphides showed superconductivity at low temperatures and the highest critical temperature T c=8.4K was observed for SrPt 3P. The analysis of specific heat C(T) for SrPt 3P shows clear evidence for very strong coupling s-wave superconductivity with a large ratio between superconducting gap Δ 0 and T c, 2Δ 0/k BT c∼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. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.108.237001

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B - Condensed Matter and Materials Physics  

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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.materresbull.2011.12.014

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c2jm32558f

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.84.174519

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.4.0_853_1

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.66.1.3.0_599_1

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica C: Superconductivity and its Applications  

Bulk superconductivity was discovered in BaRh2P2 (Tc=1.0K), BaIr2P2 (Tc=2.1K) and SrIr2As 2 (Tc=2.9K), which are isostructural to (Ba,K)Fe2As 2, indicative of the appearance of superconductivity over a wide variety of layered transition metal pnictides. The electronic specific heat coefficient in the normal state, 9.75, 6.86 and 7.03 mJ/(mol K2) for BaRh2P2, BaIr2P2 and SrIr 2As2 respectively, indicate that the electronic density of states of these three compounds are moderately large but smaller than those of Fe pnictide superconductors. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.11.059

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Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.65.1.3.0_528_3

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Physical Society of Japan  

Bulk superconductivity was discovered in BaRh2P2 (Tc = 1:0 K) and BaIr2P2 (Tc = 2:1 K), which are isostructural to (Ba,K)Fe2As2, 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 K2) for BaRh2P2 and BaIr2P2 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 RW = χ/γ × π2 kB2/3 μB2 close to 1 indeed implies the absence of strong electron correlations and magnetic fluctuations unlike Fe pnictides. ©2009 The Physical Society of Japan.

DOI： 10.1143/JPSJ.78.023706

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Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2344

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

&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

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

&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

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2079

CiNii Books

記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.1143/JPSJ.78.023706

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

CiNii Books