Yang Qiansheng

The copper isotope effect in Ba2Y Cu3O7

Abstract The effect of isotopic substitution on the superconducting Tc in the 90 K superconductors Ba2Y Cu3O7 by replacing ordinary copper Cu with 63Cu and 65Cu has been studied. The transition temperatures are found to be the same within experimental error of ± 0.2K. This indicates that the copper isotope effect is absent in this material, as in the cases of oxygen.

Josephson effects in Nb/YBa2Cu3O7-δ point contacts and YBa2Cu3O7-δ break junctions

Josephson effects have been observed in Nb/YBa2Cu3O7-? point contacts and YBa2Cu3O7-? break junctions. When the junctions are exposed to a microwave field, the I-V characteristics show constant voltage steps, the heights of which follow the Bessel function behavior. Obvious asymmetry about zero bias has been observed in YBCO break junctions which, we suggest, may possibly result from flux trapping in the complicated weak link structure of the system. Microwave-induced sub-steps have also been found in YBCO break junctions. All experiments were conducted at liquid helium temperature.

HIGH-TC SUPERCONDUCTIVITY IN NEW OXIDE SYSTEMS

Th-Ba(Pb)-Cu oxides and Th-Ba(Zr)-Cu oxides are prepared and high-Tc properties are found in these samples. Superconductivity with midpoints of the resistive transition 88.9, 86.2 K and onsets 91.3, 93 K is observed by both magnetic susceptibility and resistance measurements, respectively. The transition width, Tc(10-90%)=4.8, 7.1 K. The nominal formula of the compounds is Th5-xBaxM2-0.5xCu5O13+y, where M is Pb, Zr.

Properties of DC SQUIDs Made from YBCO and TBCCO Films

Double-microbridge dc superconducting quantum interference devices (SQUIDs) have been fabricated from the postannealed Y1Ba2Cu3Oy and Tl2Ba2Ca2Cu3Oy thin films by chemical etching and ion milling patterning technique. The applied magnetic field dependences of the voltage of the YBCO and TBCCO SQUIDs have been studied at temperature ranging from 4.2 to 23 K and at 77 K. The largest output voltage of the devices were 3.4 μV/Φ0 (at 5 K) for YBCO and 60 μV/Φ0 (at 77 K) for TBCCO. The properties of the output of these devices have been discussed.

Nonequilibrium phenomena in Sn-Sn-PbBi system placed in various sample surroundings

Nonequilibrium superconductivity and intermediate states in Sn-Sn-PbBi system have been studied in different sample surroundings of vacuum, gas helium, and liquid helium. General behaviors under quasiparticle injection are presented. Nonequilibrium quasiparticle distribution function is modeled by the μ* - T* scheme, and the phonon trapping factor τes/τB is calculated through R-T equations.

Thin films Bi(Pb)-Sr-Ca-Cu-O (Tc (zero) = 105K) prepared by ion beam sputtering

High temperature superconducting Bi(Pb)-Sr-Ca-Cu-O thin films have been deposited onto single crystals (100) MgO substrates heated at 400°C by ion beam sputtering and were post annealed in air. The film properties are sensitive to the annealing conditions. The best films show an onset transition temperature of approximately 120K and zero resistance at 105K. X-ray diffraction shows the films to have high c-axis orientation with a high Tc phase. The composition of film was determined by inductively coupled plasma-atomic emission spectrometry analysis, and their morphology was observed by scanning electron microscopy.

Observation of chaotic noise in Nb-in point contact

For the first time, the chaotic noise in point contact has been investigated in the presence of dc current and rf radiation. The I-V characteristics and the corresponding rms noise voltage are measured simultaneously. Two types of modes of chaotic noise can be identified. Interesting feature of the intermittent chaotic noise has been observed.