Flux pinning by anisotropic arrays of antidots in superconducting thin films

Anisotropic arrays of antidots have been prepared on Y-Ba-Cu-O and Nb thin films by electron-beam lithography. Fast-Fourier-Transform analysis of the magnetization curves for Y-Ba-Cu-O thin film reveals their periodical character which corresponds to the matching effect of the vortex lattice. For niobium thin film, matching peaks can be observed on the decreasing branches of the magnetization curves. Magneto-optical investigations at lower temperatures show unidirectional flux entry and exit along the shorter antidot lattice parameter. In higher magnetic fields, an anisotropic critical state is observed. Our observations strongly suggest formation of anisotropic vortex lattices in the patterned thin films.