Kosuke Tanaka

How to make superconducting-anisotropy least in high-Tc cuprate superconductors

Abstract The guiding principles to reduce superconducting-anisotropy were derived for high-T c cuprate superconductors. Based on the principles, we have attained the least superconducting-anisotropy γ=1.6 for a Cu-based CuBa 2 Ca 3 Cu 4 O 12−y (Cu-1234) superconductor. Further lower superconducting-anisotropy has been proposed for Cu-1245 (γ=1.3) and Cu-1256 (γ≌1.0) Cu-based superconductors.

Mechanism of Tc enhancement in Cu1−xTlx-1234 and -1223 system with Tc > 130 K

Abstract A new Tc enhancement method, a combination of alloying of Cu- and Tl-system and selective reduction for hole-doping has been developed for Cu 1−x Tl x Ba 2 Ca 3 Cu 4 O 12−y (Cu 1−x Tl x -1234) and Cu 1−x Tl x Ba 2 Ca 2 Cu 3 O 10−y (Cu 1−x Tl x -1223) system. The method is very effective for the Tc enhancement up to 132 K for Cu 1−x Tl x -1223 and 126 K for Cu 1−x Tl x -1234( x =0.4∼0.9). A new concept of band degeneration effect is proposed as the Tc enhancement mechanism for a common optimum hole-doping in every CuO 2 layers.

High pressure synthesis and characterization of single crystals of CuBa2Ca3Cu4Oy superconductor

Abstract Single crystals of CuBa 2 Ca 3 Cu 4 O y (Cu-1234) with dimensions up to 200×100×20 μ m 3 have been synthesized under high pressure using a belt type anvil apparatus. The impurity of Au, emanating from Au capsule, was found in the crystals by SEM–EDS analysis. These crystals showed superconducting transition temperature ( T c ) ranging from 105 K to 68 K and are lower than that of Au-free polycrystals ( T c =118 K). The T c values are found to decrease linearly with Au content at a substantially high rate of 7.0±0.4 K%, indicating the substitution of Au ions for Cu-sites. Superconducting anisotropy γ as estimated from the resistivity data of Cu-1234 single crystal just above T c (=102 K) has been found to be higher ( γ =5.8) than that for the Au-free polycrystals.