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 45° [001] tilt grain boundaries in YBa2Cu3O7 − x films. Implications for the transport properties of the grain boundaries are discussed. A model based on a dx2 − y2-wave symmetry component of the superconducting order parameter and on grain-boundary faceting is consistent with the results of our experiments. © 1996 The American Physical Society.