Flux penetration and critical current limited by material inhomogeneities in a YBCO superconducting strip

A state-of-the-art scanning If all probe microscope has been used to measur e flux profiles across one 'wire' of a long YBCO thin film meander line as a function of both transport current density and applied magnetic field. Fl ux. bundle penetration due to an applied current or magnetic field is demon strated to occur at the same disordered regions at the edge of the film. Vo rtices trapped in the strip during field cooling appear to play no role in the process of first flux penetration.