[en] The transport properties of magnesium diboride in the normal state are briefly reviewed. The temperature dependence of resistivity is explained by taking into account the contribution of E_2g optical phonon mode. From the sign of Hall coefficient, thermoelectric power, the type of predominant carriers is determined for each direction. In the Hall coefficient, the multiband effect is clearly observed, as a strong anisotropy between in-plane and out-of-plane component. In the thermoelectric power, a phonon contribution to thermal transport manifests itself

[en] By this study, a graphite calorimeter has been developed to measure the average ion energy from electrostatic ion accelerator (3 MV Tandem Ion Accelerator of the Takasaki Ion Accelerators for Advanced Radiation Application). A graphite calorimeter was designed for measuring the ion beam energy in wide ion energy ranges (from 3 MeV to 10 MeV). By a couple of this study, the ¹ H(¹⁵ N, α γ) ¹² C resonant nuclear reactions (resonant energy 6.385 MeV and 13.355 MeV) has been applied for measuring the absolute ion beam energy serve as a comparative method. The obtained results were compared in terms of resolution and accuracy. Close agreement was found for both methods, the deviation was observed within ± 3%

[en] We report resistivity and magnetization of single crystal MgB₂, focusing on the broadening of superconducting (SC) transition in magnetic fields. In-plane and out-of-plane resistivity indicate that the broadening of SC transition is independent of Lorentz force and that it is merely dependent on the magnetic field direction. In magnetization, diamagnetic signal begins to appear at almost the same temperature as the onset temperature of resistivity transition. These results suggest that the broadening is attributed not to the surface superconductivity but to the SC fluctuation or the vortex-liquid picture, owing to the short coherence length and the high transition temperature of MgB₂

[en] Lithium ion was successfully introduced into La_1/3NbO₃ with an A-site-deficient perovskite-type structure. The crystal structure and transport properties of La_1/3Li_xNbO₃ were investigated as a function of Li content (x = 0-0.59). The lattice parameters of La_1/3Li_xNbO₃ with an orthorhombic cell were enlarged with increasing Li content for x ≤ 0.3, and the structure was transformed to a pseudo-tetragonal cell for x = 0.44. The temperature dependence of electrical resistivity gradually changed from insulating to metallic with increasing x, and thermoelectric power measurement indicated that the carriers were electrons. In X-ray photoelectron spectra of the incorporated samples, Nb_3d⁴⁺ peaks appeared in addition to Nb_3d⁵⁺ peaks, which was consistent with the change of the transport properties. In spite of the success of metallization, no diamagnetic signal indicative of supercondcutivity was observed in La_1/3Li_0.59NbO₃ down to 1.8 K

[en] By controlling growing process, we have succeeded in making MgB₂ single crystals with different electronic properties. In the crystals with smaller c/a, larger residual resistivity ratio, higher T_c, and higher anisotropy in H_c2 are observed. In superconducting state, a difference of anisotropy is attributable to H_c2(parallel c), suggesting a considerable change beyond the disorder effect due to lattice strain. We discuss possible origins for the changes

[en] Effect of grain boundaries on the magnetic field distributions in YBCO was studied by use of magneto-optical (MO) imaging technique. The grain boundary was artificially introduced with a multi-seeded melt-growth process. The current distribution in the sample was obtained from the MO image using an inversion scheme based on the inverse-matrix method. With this technique, we could obtain intergranular and intragranular critical current densities. Large depression of the intergranular critical current was observed in the sample with large misorientation angles

[en] A digitally controlled emittance measurement, data acquisition and processing system has been designed, implemented and used to determine emittances of negative ion beams extracted from high-intensity negative-ion sources equipped with cylindrical and spherical geometry cesium surface ionizers. Comparative studies indicate that the emittances of ion beams extracted from the source equipped with a spherical geometry ionizer are lower by 13% to 21% than those extracted from the source equipped with a cylindrical geometry ionizer. This difference may be attributable to geometric factors rather than differences in the sizes of the emission areas at the points of negative-ion generation. Studies reveal that the emittances of these sources are independent of ion mass for most of the materials investigated and independent of ion current over the range of ion currents used in these investigations (4μA to 12 μA)

[en] The normal state electronic structure of the high-T_c cuprates is discussed, based on the optical spectra. The unique feature in the electronic states of cuprates is that the charge transfer gap is easily deformed by a small amount of doping. The strong hybridization of the Cu- and O-orbital, which may play a role in this drastic doping effect, is also evidenced by the recently observed coupling between the Cu-O vibrational phonon and the Cu-O charge transfer excitation. (orig.)

[en] We have measured the anisotropic charge dynamics in the 90-K phase of YBa₂Cu₃O_y, and have found that the out-of-plane scattering time is more than five times shorter than the in-plane scattering time. Another anomal is the rapid enhancement of the in-plane scattering time below T_c. Our magneto-thermopower measurement has revealed that the enhancement also occurs in the mixed state. These two features are never ovserved in other layered superconductors, such as organic BEDT salts or Sr₂RuO₄; thus, they can be direct evidence for the non-Fermi-liquid behavior of high-T_c cuprates

[en] Magnetic field dependence has been investigated in the c-axis optical conductivity of underdoped YBa₂Cu₃O_6.6. Under the parallel field (H parallel CuO₂ plane), an enhancement of the spectral weight was observed for the 400 cm^-1 peak, in correspondence with the reduction of the superconducting condensate weight. This supports the superconducting origin of this mode, known as the 2nd Josephson plasmon scenario proposed by van der Marel and Tsvetkov. It was also found that parallel field induces a well-defined oscillation mode at the energy scale of the Josephson plasma frequency. Similar phenomena have been observed in a bilayer cuprate Bi₂Sr₂CaCu₂O_8+δ, but not in single layer cuprate La_2-xSr_xCuO₄. Origin of this new mode is discussed