Research on High-T_c Superconductors with Relation to Anisotropy

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The research subjects of the project are (1) chemical control of anisotropy of superconductors and search for new superconducting materials, (2) elucidation of the mixed state of superconductivity in relation to anisotropy, and (3) atomic layr control in thin film fabrication and design of new superconducting devices.The results of the project are as follows.(1) Monophasic Hg_<1-x>Re_xSr_2Ca_<n-1>Cu_nO_y has been successfully prepared by high pressure synthesis. The strong pinning has been found in the material post-annealed at lower temperatures which has a superstructure due to ordering of Re and Hg. The diminution of anisotropy owing to conducting ReO_6 block may be an origin of improvement in pinning characteristics. It has been found that a dramatic increase occurs in J_c in Bi_2Sr_2CaCu_2O_y (Bi2212) single crystals doped a large amount of Pb. Electron microscope has revealed characteristic microstructure which is probably responsible for the observed enhancement in J_c. Electron … More ic state of spin ladder compound LaCuO_<2.5> and microstructure of Y_2B_4Cu_7O_<15-delta> have been investigated.(2) Using single crystals of La_<2-x>Sr_xCuO_4, YBa_2Cu_3O_<7-delta> (Y123) and Bi2212, the magnetization-temperature diagrams have been investigated in order to elucidate the vortex lattice melting transition by local mangetization, ultrasonic effect, complex susceptibility and magnetic torque measurements. The vortex lattice melting transition has been theoretically investigated. The transition of untwinned Y123 single crystal in the high magnetic field up to 23T has been clarified. A very interesting venture to observe directly vortex by sight using scanning tunneling microscopy (STM) has proceeded.(3) Control of atomic layr in thin film fabrication has progressed. The multilayr type Y123/SrTiO_3/Y123 junction has been successfully fabricated, although the Josephson effect has not been observed yet. The effect of quasi-particle injection in Y123, single crystal switching gate fabricated using cuprate superconductors, characteristics of superconductor junction by local level control, the electric field effects on transport and superconducting properties of Y123 have been investigated. Less