Research on High-T_c Superconductors with Relation to Anisotropy

该计划的研究课题是：（1）超导体各向异性的化学控制和寻找新的超导材料;（2）超导性的混合态与各向异性的关系的阐明;（3）薄膜制造中的原子层控制和新超导器件的设计。(1)用<1-x><n-1>高压合成法成功地制备了单相Hg_ Re_xSr_2Ca_ Cu_nO_y。在较低温度下退火后的材料中发现了强烈的钉扎，由于Re和Hg的有序化，该材料具有超结构。由于ReO_6的导电性，各向异性的减小可能是钉扎特性改善的原因。研究发现，大量Pb掺杂的Bi_2Sr_2CaCu_2O_y（Bi_（2212））单晶的J_c有显著的增加。电子显微镜观察到的特征显微结构可能是J_c增强的原因。电子 关于我们 研究了自旋梯型化合物LaCuO_2的电子态<2.5>和Y_2B_4Cu_7O_2的微结构<15-delta>。(2)用<2-x><7-delta>局域磁化、超声效应、复磁化率和磁矩测量等方法，研究了La_Sr_xCuO_4、YBa_2Cu_3O_（Y123）和Bi_（2212）单晶的磁化-温度图，以阐明涡旋晶格熔化转变。对涡旋晶格熔化转变进行了理论研究。阐明了非孪晶Y123单晶在高达23 T的强磁场中的相变。利用扫描隧道显微镜（STM）直接观测涡旋是一项非常有趣的尝试。(3)薄膜制造中原子层的控制已经取得了进展。成功地制备了Y123/SrTiO_3/Y123多层结，但尚未观察到约瑟夫森效应。本文研究了准粒子注入对Y123的影响，用铜氧化物超导体制备的单晶开关门，局域能级控制的超导结特性，电场对Y123输运和超导性质的影响。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