[en] Tunneling spectroscopy was performed on in-plane oriented (100)-Y_1-XCa_XBa₂Cu₃O_7-Y/In tunnel junctions. For underdoped Y₁Ba₂Cu₃O_7-Y a zero-bias conductance peak (ZBCP) was observed which did not split down to 4.2K. For optimally doped YBCO a splitting of the ZBCP at zero magnetic field was observed below 6K and a large anisotropy of the splitting was observed as a function of field orientation. The splitting of the ZBCP is strong if the magnetic field is applied parallel to the (001) direction and weak if the field is parallel to the (010) or (100) direction. The splitting shows a large magnetic hysteresis if the magnetic field is parallel to the (001) direction. For Ca-doped TBCO no ZBCP was observed. Instead a sub-gap appeared below 10K, which widened if a magnetic field is applied. The data suggests an order parameter with a complex symmetry that depends on temperature, doping level and magnetic field

[en] Temperature dependence of Hall constant R_H and longitudinal resistivity ρ_xx have been measured in Ca-doped YBCO thin films with varying oxygen contents, with emphasis on the overdoped regime. R_H vs. T data present a peak near T_c whose height reduces with doping and disappears at optimal doping. Unexpectedly, the peak reappears above optimal doping with a height that increases with doping. A similar behavior was observed in the parameters that fit cot(θ_H) vs. T to a parabola. They decrease smoothly with increasing doping in the underdoped region and present a peculiar peak in the overdoped region. This behavior might indicate the crossover to a new regime of transport properties in strongly overdoped HTSC. We discuss the possible origin and implications of these results

[en] The application of the Ginzburg criterion yields for the new high T/sub c/ oxides a broad critical region, with a width of order unity. This width could be reduced in the event of large strong coupling corrections

No abstract available

[en] A key feature of the high T/sub c/ oxides is a very small value of the Fermi energy. This feature leads to peculiar thermodynamic and transport properties in the normal and superconductive state. 24 refs., 1 fig

No abstract available

[en] It is shown that, as in the case of electric motors and generating sets, beyond a certain size it will be more economic for computers to be superconducting. The achieve this a memory element that is both faster and dissipates less power than present semiconductor ones is required. The technological difficulties of building such a memory element based on the principle of superconducting Josephson tunnelling through thin oxide barriers or other weak links are discussed. The alternative possibility of using granular superconductors to provide a memory element consisting of a weak link or bridge linking two superconductors is considered. Such a memory appears to have the basic quality of the tunnelling Josephson junction of high switching speed and is also rugged. Granular superconductors could make the superconducting computer a practical reality. (U.K.)

[en] Andreev reflections have been studied at the interface between a gold tip and La_2-xSr_xCuO₄ (x=0.11, 0.12) single crystals, along the (110) direction. The shape of the I(V) characteristic has been analyzed within the framework of the theory of Tanaka and Kashiwaya, allowing for an anisotropic order parameter. The data cannot be fitted either to a pure isotropic s-wave or pure d-wave symmetry. The best fit is obtained for an anisotropic gap, with Δ_max = 15 meV and Δ_min = 5 meV

[en] Ultrathin films of Indium, Aluminum and Gold, in intimate contact with Germanium, show interesting electrical properties. Due to good wetting properties, continuity is reached at very small thickness. Au films (8-24A) have been found to be superconducting (T/sub c/ similarly ordered 1K) with relatively high critical current density and high critical fields, and to have a reduced number of carriers with a high effective mass. The interplay between disorder and superconductivity is observed as a function of the Au film thickness

[en] Published in summary form only