Nonmagnetic Ground State in RuO_{2} Revealed by Muon Spin Rotation

The magnetic ground state of single crystalline RuO_{2} was investigated by the muon spin rotation and relaxation (μSR) experiment. The spin precession signal due to the spontaneous internal magnetic field B_{loc}, which is expected in the magnetically ordered phase, was not observed in the temperature range 5-400 K. Muon sites were evaluated by first-principles calculations using dilute hydrogen simulating muon as pseudohydrogen, and B_{loc} was simulated for the antiferromagnetic structures with a Ru magnetic moment |m_{Ru}|≈0.05μ_{B} suggested from diffraction experiments. As a result, the possibility was ruled out that muons are localized at sites where B_{loc} accidentally cancels. Conversely, assuming that the slow relaxation observed in μSR spectra was part of the precession signal, the upper limit for the magnitude of |m_{Ru}| was estimated to be 4.8(2)×10^{-4}μ_{B}, which is significantly less than 0.05μ_{B}. These results indicate that the antiferromagnetic order, as reported, is unlikely to exist in the bulk crystal.

Pinalites: Optical Properties and Quantum Magnetism of Heteroanionic A3MO5X2 Compounds

Heteroanionic compounds, which contain two or more types of anions, have emerged as a promising class of materials with diverse properties and functionalities. In this paper, I review the experimental findings on Ca3ReO5Cl2 and related compounds that exhibit remarkable pleochroism and novel quantum magnetism. I discuss how the heteroanionic coordination affects the optical and magnetic properties by modulating the d-orbital states of the transition metal ions. Subsequently, I compare these materials with other heteroanionic and monoanionic compounds and highlight the potential of A3MO5X2 materials for future exploration of materials and phenomena.

Superconductivity in High-Entropy Antimonide M1-xPtxSb (M = Equimolar Ru, Rh, Pd, and Ir)

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

Fermi surface and light quasi particles in hourglass nodal chain metal β-ReO2

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

Crystallization of heavy fermions via epitaxial strain in spinel LiV2O4 thin film

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.

Mechanism of Reductive Fluorination by PTFE-Decomposition Fluorocarbon Gases for WO3

Reductive fluorination, which entails the substitution of O^2- 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 C═C 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 WO_3-xF_x where solid-state diffusion of O^2- and F^- is discerned at 500 °C.

Successive phase transitions of the spin-orbit-coupled metal Cd2Re2O7probed by high-resolution synchrotron x-ray diffraction

The 5dpyrochlore 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 groupFd-3m), has been clearly observed and reveals the following significant facts: inversion symmetry breaking and tetragonal distortion occur simultaneously atT_s1= 201.5(1) K; the previously believed first-order transition between phase II (I-4m2) and phase III (I4₁22) atT_s2∼120 K consists of two close second-order transitions atT_s2= 115.4(1) K andT_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 representationE_uof theO_hpoint 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.

Dimensional reduction and incommensurate dynamic correlations in the [Formula: see text] triangular-lattice antiferromagnet Ca3ReO5Cl2

The observation of spinon excitations in the [Formula: see text] 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.

Characterization of the charge transfer luminescence of the [WO6]6- octahedron in Ca3WO6 and the [WO5]4- square pyramid in Ca3WO5Cl2

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.

Pyrochlore oxide Hg2Os2O7on verge of metal-insulator boundary

Semimetallic osmium pyrochlore oxide Cd₂Os₂O₇undergoes 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 Hg₂Os₂O₇through 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 Hg₂Os₂O₇is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd₂Os₂O₇. Hg₂Os₂O₇exists on the verge of the metal-insulator boundary on the metal side and provides an excellent platform for studying the electronic instability of 5delectrons with moderate electron correlations and strong spin-orbit interactions.

Possible quadrupole order in tetragonal Ba2CdReO6and chemical trend in the ground states of 5d1double perovskites

The synthesis and physical properties of the double perovskite (DP) compound Ba₂CdReO₆with the 5d¹electronic configuration are reported. Three successive phases originating from a spin-orbit-entangledJ_eff= 3/2 state, confirmed by a reduced effective magnetic moment of 0.72 μ_B, were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure atT_s= 170 K, below which theJ_eff= 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two more electronic transitions to a possible quadrupole ordered state atT_q= 25 K and an antiferromagnetic order of dipoles with a ferromagnetic moment of ∼0.2 μ_BatT_m= 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 5delectrons (2010 Chenet al Phys. Rev. B82174440). The DP Ba₂BReO₆compounds provide a unique opportunity for a systematic investigation of symmetry breaking in the presence of multipolar degrees of freedom.

Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A3ReO5Cl2 (A = Ba, Sr)

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.

Na3Pt10Si5: A Non-Centrosymmetric Superconductor Having Rattling Na Atoms in the Tunnel Framework Structure

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.

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

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.

Four anti-perovskite-type compounds, ZnNNi₃, ZnCNi₃, SnNCo₃, and SnCCo₃, are synthesised through reactions between metal oxides and organic compound melamine (C₃H₆N₆).

"Visible" 5d Orbital States in a Pleochroic Oxychloride

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.

Spin and orbital contributions to magnetically ordered moments in 5d layered perovskite Sr2IrO4

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 <L>/<S>∼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 J(eff) = 1/2 moment of a spin-orbital Mott insulator, |<J(1/2)|L(z)|J(1/2)>|/|<J(1/2)|S(z)|J(1/2)>| = 4, which cannot be accounted for by the redistribution of orbital components within the t(2g) bands associated with the elongation of the IrO6 octahedra.

Spontaneous formation of zigzag chains at the metal-insulator transition in the β-pyrochlore CsW2O6

A paramagnetic metal to nonmagnetic insulator transition at T(MIT)=210 K is reported for the β-pyrochlore oxide CsW(2)O(6), accompanied by a first order structural transition that creates <110> oriented chains in the pyrochlore lattice. Comparison of CsW(2)O(6), which has 1 electron per 2 W sites, to the fully d(0) analog CsTaWO(6) 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 β-pyrochlore phase. A further electronic instability is required to create the insulating ground state.

Strong coupling superconductivity at 8.4 K in an antiperovskite phosphide SrPt3P

We report the discovery of a family of ternary platinum phosphides APt3P (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 Δ0 and T(c), 2Δ0/k(B)T(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.

Gelled droplet vitrification improves recovery of cryopreserved potato germplasm

The droplet vitrification method was improved for maneuverability by embedding shoot tips in gelled droplets before osmoprotection. This newly modified cryopreserving method -gelled droplet vitrification - was compared with other PVS2-based cryopreservation methods using potato shoot tips. Survival rates of each cryogenic procedure held at 25 degree C were about 40 percent by cryotube-vitrification procedures (vitrification and encapsulation vitrification methods) and about 70 percent by PVS2-droplet procedures (droplet vitrification and gelled droplet vitrification methods). Much higher cooling rates of PVS2-droplet procedures than cryotube- vitrification procedures increased their survival rates. The gelled droplet vitrification method was applied to shoot tips of 26 potato cultivars and six wild potatoes. After a little modifications of the conditions for preculture, osmoprotection and dehydration, all cultivars and wild potatoes produced high enough survival rates to be of value to genebanks and all surviving shoot tips developed normal shoots within 3 weeks.

Simplified cryopreservation of sweet potato [ Ipomoea batatas (L.) Lam.] by optimizing conditions for osmoprotection

Shoot tips of sweet potato were successfully cryopreserved using an encapsulation vitrification method. Encapsulated shoot tips were pre-incubated in liquid Murashige-Skoog medium containing 30 g/l sucrose for 24 h, then precultured in sucrose-enriched medium (0.3 M sucrose) for 16 h. Shoot tips were osmoprotected with a mixture of 2 M glycerol and 1.6 M sucrose for 3 h before being dehydrated with a highly concentrated vitrification solution (PVS2) for 1 h at 25 degrees C. The encapsulated and dehydrated shoot tips were transferred to a 2 ml cryotube, suspended in 0.5 ml PVS2, and plunged directly into liquid nitrogen. Rapidly warmed shoot tips developed normal shoots and roots in 21 days without any morphological abnormalities after plating on a recovery medium. High levels (average of about 80%) of shoot formation were obtained for three cultivars of sweet potato. This encapsulation vitrification method appears promising for cryopreservation of sweet potato germplasm.

Newly developed encapsulation-dehydration protocol for plantcryopreservation

A simplified and efficient encapsulation-dehydration protocol, which is a compromise between vitrification and encapsulation-dehydration, was presented for plant cryopreservation. In this protocol, during the encapsulation process, the apices precultured with 0.3 M sucrose for 16 h were simultaneously osmoprotected with a mixture of 02 M glycerol plus 0.4 M sucrose for 1 h. These encapsulated apices were directly dehydrated with dry silica gel prior to a plunge into LN without the pretreatment of 0.8M sucrose for 16 h. This protocol produced much higher rates of recovery growth in the three plant species tested (wasabi, chrysanthemum, and mint) than those cryopreserved by the conventional encapsulation-dehydration. This protocol also considerably reduced the time needed for the cryogenic procedure. Thus, this new protocol appears promising for cryopreservation of shoot apices and other explants.

Cryopreservation of in vitro-grown axillary shoot-tip meristems of mint (Mentha spicata L.) by encapsulation vitrification

 Alginate-coated meristems from in vitro-grown axillary buds of mint (Mentha spicata L.) were successfully cryopreserved by vitrification. Excised meristems from nodal segments cold hardened at 4  °C for 3 weeks were encapsulated and osmoprotected by a mixture of 2 M glycerol plus 0.4 M sucrose. These meristems were dehydrated with a highly concentrated vitrification solution (PVS2 solution) for 3 h at 0  °C prior to a plunge into liquid nitrogen. Successfully encapsulated vitrified meristems developed shoots within a week after plating without intermediary callus formation. The average rate of shoot formation amounted to nearly 90%. This procedure was successfully applied to other Mentha species. It was also confirmed that encapsulated vitrified meristems produced a much higher rate of shoot formation than the encapsulated dried meristems. Thus, this revised encapsulation vitrification method appears promising for the cryopreservation of mint and other germplasm.

An assessment of pain and return to normal activity. Laparoscopic herniorrhaphy vs open tension-free Lichtenstein repair

BACKGROUND

Laparoscopic herniorrhaphy is controversial and deserves critical evaluation.

METHODS

In a randomized prospective study transabdominal preperitoneal laparoscopic herniorrhaphy (n = 24) was compared in patients to the tension-free Lichtenstein repair (n = 29) utilizing validated and reliable pain and activity assessment tools. The Sickness Impact Profile (SIP) was used to compare preoperative normal activity to postoperative activity. A Pain-O-Meter (visual analogue scale plus affective and sensory pain descriptors) assessed intensity of pain. The total pain assessment score and SIP were compared across time (postoperative day 1-42). Analgesic medication was used as a covariate.

RESULTS

The total pain score was less for laparoscopic herniorrhaphy but this did not reach statistical significance. Similarly, the SIP showed modest improvement for laparoscopic herniorrhaphy. No differences between groups were noted for morphine equivalents of administered analgesics or length of hospitalization.

CONCLUSION

Further investigation of laparoscopic herniorrhaphy is warranted.

Nasal Staphylococcus aureus and postoperative infection

Over a one-year period 19.5 per cent of 237 patients carried Staphylococcus aureus in their nares preoperatively. This rate was not influenced by the length of hospital stay. The patient nasal carrier state had no correlation with the incidence of postoperative infection. There was no outbreak of S. aureus infection during this period. It is well known that a long preoperative stay greatly increases the risk of infectious complications. This increase in infectious complications was not linked to nasal S. aureus colonization in this study. S. aureus was responsible for 19 per cent of postoperative infections in a 12-month period. S. aureus still occupies a significant place in nosocomial infection rates.