Research on High-T_c Superconductors with Relation to Anisotropy

本项目的研究内容包括：(1)超导体各向异性的化学控制和新型超导材料的寻找；(2)超导混合态与各向异性的关系；(3)薄膜制备和新型超导器件设计中的原子层控制。在较低温度下退火后的材料中发现了较强的钉扎，由于Re和Hg的有序，材料具有超结构。导电ReO_6块体引起的各向异性减小可能是钉扎特性改善的原因之一。研究发现，在掺入大量铅的Bi2Sr2CaCu2Oy(Bi2212)单晶中，J_c显著增加。电子显微镜显示了特殊的微观结构，这可能是观察到的J_c.电子…增强的原因研究了自旋梯形化合物LaCuO_(2.5)和Y_2B_4CuO_7O_(15)的微观结构.(2)用La_xCuO_4、YBa2Cu3O_(2.5)和Bi2212单晶研究了磁化温度图，用局域磁化、超声效应、复磁化率和磁矩测量解释了涡旋晶格熔化转变.对涡旋晶格熔化转变进行了理论研究。阐明了未孪晶的Y123单晶在23T强磁场中的相变。利用扫描隧道显微镜(STM)直接观察旋涡的有趣尝试已经进行。(3)薄膜制备中原子层的控制取得了进展。虽然还没有观察到约瑟夫森效应，但Y123/SrTiO3/Y123多层结已经成功制备。研究了Y123中准粒子注入、铜酸盐超导体单晶开关门、局域能级控制超导结特性、电场对Y123输运和超导特性的影响。较少

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