Magnetooptical investigations of large transport currents in Y-Ba-Cu-O-thin films

Inhomogeneities in large area YBCO-thin films can be studied in external magnetic fields with a specially designed magnetooptical apparatus. Moreover, an investigation of transport current induced magnetic fields in patterned HTS-thin films is possible as well. In the present work we studied the flux penetration of the current induced fields into YBCO-bridges of 8 × 0.7 cm² dimensions as a function of the applied currents at 77 K. For the first time transport currents up to I_tr ∼ 60 A could be investigated magnetooptically in HTS-thin films. Flux penetration starts just above a threshold value of the applied current I_tr/I_c ≥ 0.3. The influence of the bridge geometry and of inhomogeneities on flux penetration has been investigated. Flux and therefore current distributions change drastically with increasing bend-angle of the YBCO-path. A magnetic interaction between adjacent bridges with parallel and antiparallel current directions as well as a thermal interaction could be observed.