Self-generated magnetic flux in YBa2Cu3O7Àx grain boundaries

Grain boundaries in high-Tc cuprates are interesting and important for both fundamental physics and applications of high-temperature superconductivity. Conventional models of strongly coupled Josephson junctions are applicable to describe electromagnetic properties of grain boundaries in thin films of high-Tc superconductors. 4,5 A remarkable exception of this rule is the @001#-tilt boundary in YBa2Cu3O72x films with a misorientation angle close to 45°. Indeed, these grain boundaries have an anomalous dependence of the critical current Ic on an applied magnetic field Ha . Contrary to a usual Fraunhofer-type dependence Ic(Ha) with a major central peak at Ha50 and minor symmetric side-peaks the asymmetric 45° @001#-tilt grain boundaries demonstrate a pattern without a central dominant peak. Instead two symmetric major side peaks appear at certain applied magnetic fields Ha56HspÞ0. 6–11