Bitter Decoration Patterns of Y-System Thin Films

In order to evaluate pinning centers in high Tc superconductors, Bitter decoration technique was applied to Y-system thin films and a Bi2212 single crystal. Y-system thin films had irreguar flux line lattice. It may come from the fact that each fluxoid is individually pinned by a-axis oriented crystal grains or low-angle grain boundaries. On the other hand, the Bitter pattern of the Bi2212 single crystal had almost regular flux line lattice. Some disorder present is probably due to collective pinning of weak randomly distributed defects such as oxygen vacancies.