Generation of Magnetic Flux by Single Grain Boundaries of YBa2Cu3O(7-x)

Using scanning SQUID microscopy, we have directly imaged spontaneously generated delocalized magnetic flux in grain boundaries in YBa2Cu3O(7-x) films. The flux was observed in asymmetric 45 degrees [001] tilt boundaries, and could not be found in reference samples with symmetric or lower angle boundaries. Implications for the transport properties of the grain boundaries are discussed. The flux will weaken signatures of unconventional symmetry components of the superconducting order parameter. A model based on a d(x2-y2)-wave symmetry component and on grain-boundary faceting is consistent with the results of our experiments.