[en] Voltage-current characteristics, dc and ac to 75 kHz, were measured for samples of commercially supplied tapes over 100 m long of Ag- clad Bi(2223) at room temperature and at 77K. Currents to 30 A were applied. The dc critical current (the current at 0.1, μV/cm) was determined to be over 10 A and the dc resistance per length was in the range of 40 mΩ/m

[en] This paper reports that when speed of input signal of tunnel Josephson junction approaches its plasma period constant r_p, the dynamic behavior of Josephson junction exhibits interesting features. An example of such behavior is punchthrough effect. This effect arises in speed resetting process when the junction, being initially in voltage state, is resetted into zero voltage state via lowering gate current. When speed of lowering gate current is comparable with r_p, the unction instead of transition into zero voltage state transits into finite voltage state with opposite polarity. The reason of such behavior is the fact that in the nonzero voltage state the Josephson junction has sufficient energy to overrun energy barrier and punchthrough into voltage state. The authors have investigated similar effect where, however, opposite to punchthrough effect we suppose the Josephson junction to be initially in the zero voltage state i.e. average junction voltage V = 0. Application of high speed step-like current pulse can induce switching into voltage state even if the applied signal does not cross the value of critical current of the junction I₀. The effective reduction of critical current occurs due to the dynamic process

[en] Magnetic hysteresis and transverse ac permeability measurements in Bi₂Sr ₂CaCu₂O_8+δ allow a comparative analysis of the critical current with the elastic response of vortex structures, in equilibrium with their pinning potential, in the field and temperature region where the second peak is detected. This study provides strong evidence that the second peak has its origin in changes of the elastic equilibrium properties of the vortex structures

[en] We were able for the first time to calculate the critical current in a Josephson junction, under the influence of a magnetic field. This was accomplished for the general case and without any preliminary assumptions on the self-induced field. Based on these calculations, we were also able to retrieve the spatial distribution of the critical current in the junction, given its magnetic field dependence. The junction size can be large compared to the global penetration depth γ_J, and the self induced field does not have to be neglected. The calculation of the critical current as a function of the external magnetic field, I_c(H), is based on the DC Josephson effect. Here the phase difference across the junction is related to the magnetic field. If the spatial distribution of the critical current, j_c(x), is known, then I_c(H) = ∫_-∞^∞dx j_c(x) exp{2πi F[j_c(x)]} We can now calculate numerically a sample of critical currents for simulated distributions. Results can be compared very favourably with calculations made by others [2] under the assumption of a global penetration depth γ_J. In addition, we use the spatial dependence of the penetration depth to yield more accurate results

[en] Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa₂Ca₂Cu₃O_x films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a-and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density J_c varies widely, being up to 10 times as great as the transport J_c (scale of ∼ 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport J_c is largely determined by a few high-angle boundaries. 9 refs., 3 figs

No abstract available

[en] Critical-current density (J_c) is a parameter of primary importance for potential applications of high-temperature copper oxide superconductors. It is limited principally by the breakdown of zero-resistive current due to thermally activated flux flow at high temperatures and high magnetic fields. One promising method to overcome this limitation is to introduce efficient pinning centers into crystals that can suppress the flux flow. A marked increase in J_c was observed in Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) single crystals doped with a large amount of Pb. By electron microscopy, characteristic microstructures were revealed that probably underlie the observed enhancement in J_c: thin (10 to 50 nanometers), platelike domains having a modulation-free structure appeared with spacings of 50 to 100 manometers along the b axis. 30 refs., 4 figs

[en] Ag-sheathed SmFeAsO_0.7F_0.3-δ (Sm-1111) superconducting wires were prepared by a one-step solid state reaction at temperatures as low as 850-900 ⁰C, instead of commonly used temperatures of 1150-1250 ⁰C. The x-ray diffraction pattern of the as-sintered samples is well indexed on the basis of the tetragonal ZrCuSiAs-type structure. We characterized the transport critical current density J_c of the SmFeAsO_0.7F_0.3-δ wires in increasing and subsequently decreasing fields, by a resistive four-probe method. A transport J_c as high as ∼ 1300 A cm^-2 at 4.2 K and self-field has been observed for the first time in Sm-1111 type polycrystalline superconductors. The J_c also shows a rapid depression in small applied fields as well as a magnetic-history dependence, indicating weak-linked grain boundaries. The low-temperature synthesis method can be very beneficial for fabricating the RE-1111 iron oxypnictides in a convenient and safe way.

No abstract available

[en] Critical current of inhomogeneous intergranular Josephson transition is calculated in the assumption concerning superconductivity suppression by local strains of boundary dislocations with random distribution