Trapping state of quantized vortices in high-T-c YBa2Cu3O7-y thin films observed by scanning SQUID microscope

Magnetic field images of YBa2Cu3O7-gamma thin films are observed at various temperatures using scanning SQUID microscope. The observed magnetic flux c arried by one vortex quantitatively agreed with the value of one flux quant um Phi (0) (= 2.07 x 10(15) Wb). In the temperature between 4 K and T-c, th e distribution of quantized vortices remained unchanged. Under the presence of transport current less than the film critical current, it was also unch anged. However, for the transport current exceeding the critical value, the generation of new vortices was observed. The results demonstrate that the magnetic flux dynamically threads through a film in the flux-flow state, wh ile in the Meissner state, the flux is trapped at some pinning sites and mo re static. (C) 2001 Elsevier Science B.V. All rights reserved.