BEHAVIOUR OF ORIENTED POLYCRYSTALLINE YBaCuO SUPERCONDUCTING THIN FILMS IN A WEAK MAGNETIC FIELD

We determined a few characteristics of granular superconductivity through magnetoresistance measurements made on oriented polycrystalline YBaCuO superconducting thin films, and found that, at 77.3 K, the critical field for breaking a major portion of the superconducting weak links between grains was about 80 G, while the average lower critical field of the grains was about 175 G. Detail analyses on flux flow resistance show that a maximum of the increasing of flux flow resistance induced by a unit field will exist at a specified temperature, which we think is related to the dependence of the pinning energy on the temperature.