Flux penetration into YBa2Cu3Ox thin films covering substrate step edges

Using the high-resolution Faraday effect, the flux penetration into YBa2Cu3Ox thin films grown over one or two substrate step edges is directly observed at a temperature of T=5 K. The regions at the steps are easily penetrated by the flux already present at low applied external magnetic fields due to the locally enhanced stray fields. The step edges are found to separate the sample magnetically into independent parts. It is also shown that the local observation of flux penetration allows detection of the influence of defects in the thin-film samples on the domain structures in a direct way.