Research on High-T_c Superconductors with Relation to Anisotropy

本项目的研究课题为：(1)超导体各向异性的化学控制和寻找新的超导材料；(2)与各向异性有关的超导混合态的阐明；(3)薄膜制备中的原子层控制和新型超导器件的设计。项目结果如下：(1)高压合成成功制备了单相Hg_<1-x>Re_xSr_2Ca_<n-1>Cu_nO_y。在低温退火后的材料中发现了较强的钉钉作用，其上层结构是由Re和Hg的有序结构引起的。由于导电ReO_6块体，各向异性的减小可能是钉钉特性改善的原因。发现在Bi_2Sr_2CaCu_2O_y （Bi2212）单晶中掺杂大量Pb后，J_c急剧增加。电子显微镜观察到的特征微观结构可能是J_c增强的原因。研究了自旋阶梯化合物LaCuO_<2.5>的电子态和Y_2B_4Cu_7O_<15- δ >的微观结构。(2)利用La_<2-x>Sr_xCuO_4、YBa_2Cu_3O_<7- δ > (Y123)和Bi2212单晶，通过局部磁化、超声效应、复磁化率和磁转矩测量，研究了涡旋晶格熔化转变的磁化温度图。对涡旋晶格熔化跃迁进行了理论研究。澄清了Y123单晶在高达23T的高磁场下的转变过程。利用扫描隧道显微镜（STM）直接观测涡旋是一项非常有趣的探索。(3)薄膜制造中原子层的控制有了新的进展。虽然尚未观察到约瑟夫森效应，但已成功制备了Y123/SrTiO_3/Y123多层结。研究了准粒子注入对Y123、铜超导体单晶开关栅的影响、局域能级控制的超导体结特性、电场对Y123输运和超导性能的影响。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