Vortex matter in a thin film of YBCO with columnar indentations-very small and moderate field regimes

Interaction of vortex matter with an array of antidots was studied in the presence of very low to moderate applied fields. The physical system employed is a good-quality thin film of YBCO, pierced with a set of 1500 columnar-like indentations of nearly triangular cross section, forming a face-centered square lattice. In the very low flux regime, up to 330 mOe, the sparse matter of fluxoids was created by exposing the sample to a projection of Earth's field. The field component perpendicular to the plane of the film is largely amplified in the Meissner state and, as flux avalanches invade the sample, the amplification factor is reduced in a step-like manner.