Growth and characterization of evaporated thin films of Y1Ba2Cu3Ox

We have prepared thin films of Y-Ba-Cu-O by coevaporation in the presence of oxygen onto room-temperature substrates, followed by postannealing in oxygen. Films have been grown on (100) SrTiO₃, (100) MgO, and LiNbO₃. The films have been characterized by electrical resistivity, X-ray diffraction, and elastic backscattering (EBS) measurements.     

Microwave absorption in high-T c superconductors

We have investigated the 9- and 10-GHz microwave properties of bulk samples of strontium and barium substituted La₂CuO₄ and YBa₂Cu₃O₇ and one YBa₂Cu₃O₇ MBE film on SrTiO₃. Anomalous microwave absorption is seen especially for poorly compacted bulk ceramic samples. Transitions were generally broadened nearT _c and the residual losses were high. The real part of the surface impedance could be fit belowT _c to the empirical equation with an added term linear in temperature. The microwave response of the film was masked by paraelectric absorption and acoustic resonances in the substrate.     

Superconductivity above 100K in compounds containing Hg

Several members of a new family of (Hg,Tl)(Ba,Sr)CaCuO high temperature superconductors have been synthesized. These compounds, which are analogs to the Hg-Ba-Ca- and Tl-Ba-Ca-layered cuprates, are multi-phased and have superconducting transition temperatures above 100K. Several samples with a nominal composition of HgTl₂Ba₄Ca₄Cu₆O_y had T_cs near 130K. Details of the characterization of these samples are presented.     

Color indicator of cuprate superconductivity observed by polarized light microscopy

A common mineralogical technique for identifying individual crystals in a heterogeneous, polycrystalline sample involves the observation at room temperature of their colors in reflected polarized light (colors of polarization). Here we present the observation that a brownish yellow (golden) color of polarization is not only characteristic of the YBa₂Cu₃O₇ superconductor, but of the cuprate superconductors in general and is correlated with the occurrence of superconductivity.     

Pressure dependence of Tc in Tl0.2Hg0.8Ba2Ca2Cu3Ox

We report results of our study of the pressure dependence of T_c in Tl_0.2Hg_0.8Ba₂Ca₂Cu₃O_x to 6 GPa in a diamond anvil cell. The sample studied has an ambient T_c of 136.4 K and application of quasihydrostatic pressure raised T_c to 144.4 K at 6 GPa. We will also describe recent modifications of our ac susceptibility apparatus that have improved our sensitivity while simplifying the coil design and the balancing.