Q.S. Yang

Single crystal growth of superconducting compound Bi-Ca-Sr-Cu-O

We have prepared two kinds of single crystals in Bi-Sr-Ca-Cu oxides by flux method;plate-like single crystals which exhibit metal to superconductor at 93 K, being the high-Tclayered compound BiSr (Ca0.35Sr0.25Bi0.40)2Cu2Oy with orthorhombic structure with a=5.42 A, b=5.44 A and c=30.78 A respectively, and another kind of bar-shapedbismuth-poor single crystals which is superconducting at the temperature below 82K whilebeing semiconducting above this temperature.

High-Tc superconductivity above 110 K in the Tl-Ba-Ca-Cu-O system

High-Tc superconductivity above 110 K has been observed in Tl-Ba-Ca-Cu oxides. The dependence of electrical resistivity and AC magnetic susceptibility on temperature show that the zero-resistance transition temperature is about 114 K and a dramatic magnetic susceptibility drop appears at 117 K. The superconductivity remains stable after several cooling and heating cycles. The observation of superconductivity in this system was carried out at least eight times.

MEASUREMENT OF ANISOTROPIC THERMOPOWER IN SINGLE CRYSTALS Bi2Sr2CaCu2Oy

The thermopower in single crystals of the high Tc superconductor Bi2Sr2CaCu2Oy has been measured in both a-b plane (Sab) and along c axis (Sc) respectively. The temperature dependences are distinctly anisotropic. Sc increases monotonously with temperature and is positive from Tc to room temperature, while Sab increases rapidly near Tc and then decreases with temperature. The maximum of Sab is at 115 K and Sab changes its sign at 250 K.

WEAK FIELD MAGNETIZATION AND SUSCEPTIBILITY FLUCTUATION IN Bi2Sr2CaCu2Oy SINGLE CRYSTALS

Some magnetization curves of single crystal of Bi2Sr2CaCu2Oy in low magnetic field H ‖ c axis are given. The magnetization loop is getting smaller with the temperature increase and then disappears at temperature even higher than Tc. The experimental measurements of the susceptibility in zero-field limit show that the results can be treated with two-dimensional thermo-fluctuation theory.

X-ray diffraction study of the modulated structure in superconducting single-crystal Bi sub 2 Sr sub 2 CaCu sub 2 O sub y

This paper reports that x-ray precession technique has been utilized to study the reciprocal space of the superconducting single crystal Bi{sub 2}Sr{sub 2}CaCuO{sub y}. An average structure with space group of Pnnn and a real structure with the superspace group of P{sub 111}{sup Pnnn} or P{sub 1S1}{sup Pnnn} have been found for this one dimensional modulated incommensurate material. As well, a basic structure with the space group of Fmmm is derived from the experimental data.

120 K SUPERCONDUCTOR TlBaCaCu2Oy

We have prepared 120 K superconductor in Tl-Ba-Ca-Cu oxide system. This 120 K superconductor has been investigated by x-ray diffraction and EDAX micro-analysis. EDAX analysis shows that the composition of this superconductor is very close to TlBa(Ca1−xCux)CuOy(x−0.3). Most of the x-ray powder diffractions including all the strong ones can be indexed according to a tetragonal structure with a=5.46 A and c= 36.2 A which means that the sample is nearly a single phase material.

TUNNELLING JUNCTIONS OF SINGLE CRYSTAL BCSCO/SN FILM

The single particle tunnelling junctions consisting of single crystal BCSCO and Sn film counter electrode have been prepared. The I-V and dI/dV-V characteristics have been measured. Observed value of the energy gap is 23 meV which corresponds to 2Δ/kTc of 6.0, much larger than the BCS weak-coupling limit of 3.52.

THE RELATION BETWEEN SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE OF Tl-Ba-Ca-Cu-O SYSTEM

It was found that the same compositional samples showed different superconducting behavior and diffraction patterns due to different heat treatment. It is interesting to note that there exist at least three superconducting phases in Tl-Ba-Ca-Cu-O system. All of them belong to the space group . They have the same lattice constant a but different lattice constant c. The transition temperature Tc is closely related with the lattice constant c. The superconducting phase with bigger lattice constant c has higher Tc. A structure model, which can generalize all of the structure of high Tc superconductors, is proposed.

Fabrication and character of reproducible high quality steps and step-edge junctions on STO substrates

Abstract We report a reproducible procedure to fabricate high quality steps and step-edge junctions on SrTiO3(STO) substrate. The dynamic process of Ion Milling(IM) was simulated in theory, there exists a maximum slope angle for the steps prepared from ion milling. For 500eV Ar+ bombarding STO system, the angle is about 73°. High quality steps can be acquired with new technique procedure. Voltage modulation is about 10μV for a typical DC-SQUIDs fabricated on this type of substrate.

Tunneling studies of Nb/Al superconducting proximity-effect bilayers

Abstract Nb / Al AlO x Ti tunneling junctions with fixed Nb and Ti thicknesses of 200 nm and Al thickness ranging from 10 to 70 nm were fabricated. Preliminary results on the measurements of I – V characteristics at T = 1.3 K are reported, and are compared with a proximity-effect model recently proposed by Golubov et al. .