T. Nakanishi

Electrical conductivity and superconductivity of LaT4As12(T=Fe, Ru and Os) with skutterudite-type structure

Abstract Ternary metal arsenides LaT 4 As 12 (T=Fe, Ru and Os) with a skutterudite-type structure have been prepared at high temperatures and high pressures. These arsenides showed the superconducting transition at around 10.3xa0K for LaRu 4 As 12 and 3.2xa0K for LaOs 4 As 12 . The T c s of both these arsenides are considerably higher than those of the corresponding phosphides. LaOs 4 As 12 is a new superconductor. On the other hand, LaFe 4 As 12 did not show the superconducting transition down to 2xa0K.

Metal to insulator transition of filled skutterudite PrRu4P12 at low temperatures and high pressures

Abstract X-ray diffraction of a single crystal of PrRu4P12 has been studied at ambient pressure. PrRu4P12 has a filled skutterudite-type structure; space group: Im3, lattice constant: a=8.055(4)xa0A, Z=2, Dcalc=5.826xa0g/cm3. Positional parameters and interatomic distances in the phosphide were determined. By use of synchrotron radiation, powder X-ray diffraction patterns of PrRu4P12 were measured up to 50xa0GPa at room temperature. The lattice constant monotonically decreases with increasing pressure. The cell volume vs. pressure curve for PrRu4P12 is fitted with the Birch equation of state. The bulk modulus of the phosphide is 207±12xa0GPa. The resistivity of PrRu4P12 was measured as a function of temperature at high pressures. The metal to insulator transition is found at around 62xa0K under ambient pressure. The transition temperature (TMI) rapidly increases with pressure at the rate of about 0.9xa0K/GPa up to 4.5xa0GPa. Above 6xa0GPa, TMI abruptly decreases with increasing pressure. The semiconductor-like behavior below TMI for PrRu4P12 is markedly suppressed at around 8xa0GPa. The metal to insulator transitions at low temperatures and high pressures are discussed.

A technique for precise magneto-transport measurements at low temperatures under pressure up to 8 GPa

Abstract A technique for a precise transport measurement under high pressure up to 8 GPa in a superconducting magnet has been developed. In order to obtain a quasi-hydrostatic pressure the direct compression method is applied to modified-Bridgman anvils with a Teflon capsule. This technique enables us to measure the absolute values of electrical resistivity, magneto-resistance and the Hall coefficient at various temperatures from 300xa0K down to 1.5xa0K in magnetic fields up to 20xa0T. We demonstrate some experimental results of magneto-transport measurements on single crystals of SmS and CeSb, showing extraordinary behavior in the temperature, pressure and magnetic field-dependent transport phenomena.

Upper critical field of spin-ladder Sr2Ca12Cu24O41

Abstract We report the upper critical magnetic field, Hc2(T), of the spin-ladder Sr 14−x Ca x Cu 24 O 41 (x=12) single crystal, which becomes superconducting above ∼3.0xa0GPa. From the measurements of the temperature dependence of AC susceptibility at 4.0 GPa in magnetic fields applied along the a-axis (⊥ ladder), the b-axis (⊥ ladder-plane) and the c-axis (|| ladder), we have determined Hc2(T) for these three directions down to about 1.6xa0K. A clear difference is observed among these three curves, indicating that this system has an anisotropic superconducting ground state.

Non-Fermi-liquid behaviour around the magnetic quantum critical point in UGa3

We studied the electronic state of UGa3 by measuring the electrical resistivity under pressure. When pressure is applied to UGa3, the Neel temperature TN = 67 K decreases steeply and becomes zero around 2.6 GPa. Correspondingly, the coefficient A in the electrical resistivity ρ = ρ0 + AT2, which is characteristic for Fermi liquid, increases steeply with increasing pressure. Around a magnetic quantum critical point of 2.6 GPa, a non-Fermi-liquid behaviour is found, showing a linear T-dependence of the resistivity, although the Fermi-liquid behaviour recovers above 4 GPa and the A-value decreases with increasing pressure. Furthermore, a resistivity drop, which might be related to superconductivity, was found below 0.3 K at 1.5 GPa, where the residual resistivity ρ0 has a maximum.

High-Pressure Transport Properties of the Superconducting Spin-Ladder System Sr14-xCaxCu24O41+δ

We report the electrical resistivity, the Hall coefficient, R H , and the magnetoresistance, MR, at pressures up to 2.0 GPa, of the spin-ladder compound Sr 14- x Ca x Cu 24 O 41+δ , on both a polycrystal ( x = 13.6) and single crystals ( x = 11 and 12), in which superconductivity has been observed only in a range of both Ca content (∼11 < x < 14) and pressure (∼1.5 < P < ∼8 GPa). The pressure dependence of the R H , with positive sign, indicates that carrier density increases with increasing pressure and localization of hole carriers at low temperature is substantially suppressed by applying pressure. We have also found that a positive MR, which violates Kohlers rule, seems to appear below the temperature at which a spin gap begins to open and strongly depends on the temperature as well as both on Ca content and applied pressure, suggesting that this MR is closely related to the mobile holes in the spin singlet state.

Dielectric dispersion in BaTiO3 single crystal at low temperatures

Abstract The dielectric constants of BaTiO3 single crystals grown by a flux method and a top seeded solution growth (TSSG) method have been reexamined in a wide temperature range of 15K–450 K and in a frequency range of 30 Hz–1 MHz. A low frequency dielectric dispersion with an intensity of Δ έ ≈1500 appears at around 100 K only on the crystals grown by the TSSG method. Results of an electric field cooling treatment on the (100) c or (111) c plates indicate that the dispersion is not due to usual domain-wall motions.

Pressure-induced structural-phase transition of CeRu2

Abstract Electrical resistivity of cubic Laves-phase compound CeRu 2 has been measured from 3 to 300 K under the quasi-hydrostatics pressure P from 1.5 up to 8 GPa. X-ray diffraction was performed at room temperature under the pressure up to 15 GPa. Temperature dependence of electrical resistivity ρ ( T ) shows no anomaly at pressures below 5 GPa and resistivity decreases with increasing pressure. However, ρ ( T ) curves, measured under the pressure above 5.5 GPa, reveal an abrupt decrease at critical temperature T a . This indicates that a new phase is induced by the pressure. T a shows a large pressure dependence: Δ T a /Δ P =59.2 K/GPa. According to the X-ray data, the phase transition above 5.5 GPa is a structural-phase transition.

Pressure effect on antiferromagnetic ordering in UIn3

Pressure phase diagram of the antiferromagnet UIn 3 was constructed from the electrical resistivity measurement under high pressures up to 9 GPa. A Neel temperature increases monotonically with inc...

Spin and Charge Dynamics in the Hole-Doped Two-Leg Ladder Compound Sr14−xCaxCu24O41

Our experimental results obtained with the doped ladder material Sr2.5Ca11.5Cu24O41 have been reviewed. Our main conclusions are 1) anisotropic resistivity under high-pressure has been measured on the single crystal. The crossover behavior of the charge dynamics from 1D to 2D in this system has been emphasized. 2) The spin gap values have been obtained for the different Ca concentrations with the neutron scattering experiments. Their values are about 32 meV, being independent of Ca concentrations and pressure up to 2.1 GPa. 3) The antiferromagnetism in the Sr2.5Ca11.5Cu24O41 at ambient pressure has been found by the specific heat and neutron scattering measurements. The relationship between antiferromagnetism and spin gap state was discussed.