  High-resolution scanning superconducting quantum interference device (SQUID)
microscopy was used to study the flux quantization phenomenon in
multiply-connected anisotropic high-Tc NdBa2Cu3O7-d single crystalline thin
films. The spatial distribution of internal flux in a hole was found to be
non-uniform and changed drastically for applied small fields. With increased
fields above 10uT, a local magnetic dipole flux developed inside the hole, in
contrast to an isotropic Nb superconductor. The total net flux trapped in a
hole was kept to be constant for larger holes, but the abrupt transition of
flux quantization state was observed for smaller holes. The possible
explanation is given based on the anisotropic dx2-y2-wave order parameter of
high-Tc superconductors.
