Kunihiko Oka

Phase-Equilibrium Diagram in the Ternary System Y2O3-BaO-CuO

A phase-equilibrium diagram of the ternary system of Y2O3-BaO-CuO was investigated. The temperature vs concentration diagrams are given on four binary systems ranging from YBa2Cu3O7-y to CuO, to BaCuO2·3CuO, to 3BaCuO2·4CuO and to 3BaCuO2·2CuO mixtures. A liquidus line required for the preparation of YBa2Cu3O7-y single crystal from solution was found to be extremely narrow in concentration range.

Laser Based Angle-Resolved Photoemission, the Sudden Approximation, and Quasiparticle-Like Spectral Peaks in Bi2Sr2CaCu2O8+δ

A new low photon energy regime of angle resolved photoemission spectroscopy is accessed with lasers and used to study the superconductor Bi2Sr2CaCu2O8+delta. The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy - the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink and associated weight transfer are robust to a possible breakdown of the sudden approximation.

Doubling of the Bands in Overdoped Bi2Sr2CaCu2O8 + delta: Evidence for c-Axis Bilayer Coupling

We present high resolution angle resolved photoemission data of the bilayer superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) showing a clear doubling of the near E(F) bands. This splitting approaches zero along the (0,0)-->(pi,pi) nodal line and is not observed in single layer Bi(2)Sr(2)CuO(6+delta) (Bi2201), indicating that the splitting is due to the long sought after bilayer splitting effect. The splitting has a magnitude of approximately 75 meV near the middle of the zone, extrapolating to about 110 meV near the (pi,0) point. The existence of these two bands also helps to clear up the recent controversy concerning the topology of the Fermi surface.

Bulk Superconductivity in Single Crystals of PrBa 2Cu 3Ox

We report the observation of bulk superconductivity in PrBa2Cu3Ox single crystals for the first time. These samples were grown by the travelling-solvent floating-zone (TSFZ) method in oxygen-reduced atmosphere. The as-grown crystal has a longer c-axis lattice constant an than any values previously reported for oxygen-reduced PrBa2Cu3Ox . After oxygen annealing, resistivity becomes zero below T=80 K, and zero-field-cooled magnetization shows diamagnetism with full volume fraction. X-ray energy dispersion spectrum and X-ray diffraction analyses show that this superconducting phase is orthorhombic PrBa2Cu3Ox .

Phase Diagram and Crystal Growth of Superconductive (NdCe)2CuO4

Single crystals of (NdCe)2CuO4 have been grown by the travelling-solvent floating-zone (TSFZ) method. The single crystal grown in a deoxidized atmosphere exhibits superconductivity. Part of the crystallographic phase diagram of the Nd2O3-CuO system has been derived by conventional means to determine the concentration and temperature range of the liquidus line.

Crystal growth of ZnO

Abstract Centimeter-sized crystals of zinc oxide have been grown by the top-seeded solution growth method and traveling-solvent floating-zone method using a mixed solvent of V 2 O 5 +B 2 O 3 and MoO 3 +V 2 O 5 . The crystals were brown, pale yellow and white semi-transparent in color depending on the solvent used. The characterization of the crystals by scanning electron microscopy X-ray energy-dispersion spectroscopy is reported.

Crystal growth of REBa2Cu3O7−y (RE=Y, La, Pr, Nd and Sm) by the travelling-solvent floating-zone method

Abstract Single crystals of REBa2Cu3O7−y (RE=Y, La, Pr, Nd and Sm) have been grown successfully by the travelling-solvent floating-zone (TSFZ) method. The maximum dimensions of the grown boules were 6 mm O×27 mm. It is shown that the density of the feed rod and atmosphere are the crucial variables for a successful growth procedure. The grown crystals were identified to be single-crystal REBa2Cu3O7−y by Laue X-ray measurements and X-ray powder diffraction. The maximum area of the grains was about 1×1 mm2 for the Y system, 1.5×1.5 mm2 for the La, Pr and Nd systems and 1.5×3 mm2 for the Sm system, respectively. Superconducting transitions of crystals annealed in oxygen typically occur at 91.5 K, 90 K, 91 K and 94 K for the Y, La, Nd and Sm compounds, respectively.

Growth and characterization of the isotopically enriched 28Si bulk single crystal

We report on the successful growth of an isotopically enriched 28Si bulk single crystal of the size ~4 mm in diameter and ~50 mm in length. The isotopic enrichement of 28Si (99.924 at%), 29Si (0.073 at%), and 30Si (0.003 at%) has been determined by secondary-ion-mass spectroscopy (SIMS). The crystal is entirely p-type with the room temperature free-hole concentration ~ 5×1017 cm-3. The majority impurity is found to be aluminum which can be removed easily in the future zone purification process.

Phase Diagram of the La2O3-CuO System and Crystal Growth of (LaBa)2CuO4

Single crystals of (LaBa)2CuO4 were grown by the top-seeded solution growth (TSSG) method. A crystallographic phase diagram of the La2O3-CuO system was derived by means of differential thermal analysis, quenching technique and X-ray diffraction.

Electric Polarization Induced by Néel Order without Magnetic Superlattice: Experimental Study of Cu3Mo2O9 and Numerical Study of a Small Spin Cluster

We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one-dimensional spin system induces electric polarization. In this system, the effects of low dimensionality and magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field–temperature phase diagram of Cu 3 Mo 2 O 9 by studying the dielectric constant and spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change in the direction of electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in a small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism.