Self-generated magnetic flux in YBa2_2Cu3_3O7−x_{7-x} grain boundaries

Grain boundaries in YBa$_2$Cu$_3$O$_{7-x}$ superconducting films are considered as Josephson junctions with a critical current density $j_c(x)$ alternating along the junction. A self-generated magnetic flux is treated both analytically and numerically for an almost periodic distribution of $j_c(x)$. We obtained a magnetic flux-pattern similar to the one which was recently observed experimentally.Comment: 7 pages, 3 figure

Paramagnetic effect in YBaCuO grain boundary junctions

A detailed investigation of the magnetic response of YBaCuO grain boundary Josephson junctions has been carried out using both radio-frequency measurements and Scanning SQUID Microscopy. In a nominally zero-field-cooled regime we observed a paramagnetic response at low external fields for 45 degree asymmetric grain boundaries. We argue that the observed phenomenology results from the d-wave order parameter symmetry and depends on Andreev bound states.Comment: To be published in Phys. Rev.

Biepitaxie-Josephson-Kontakte und Hoechstfrequenzleitungen aus YBa_2Cu_3O_7_-_#gamma#

YBa_2Cu_3O_7_-_x thin films on silicon-on-sapphire substrates have been deposited by means of electron beam evaporation and laser ablation. Double buffer layers ot yttria stabilized ZrO_2 and CeO_2 were used to improve crystalline quality and dielectric properties. Biepitaxial Josephson contacts on MgO substrates with CeO_2 buffer layers were grown. Experimental results are given for the magnetic field dependence of the critical current and the high-frequency conduction of such contacts116 refs.Available from TIB Hannover: RA 831(3076) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman