Flux Motion Dynamics and Self-Organized Criticality in YBCO Thin Films

The analytical approximated result of the flux noise in mixed state under the current driving force is derived. The Anderson-Kim flux creep model is used to relate this noise to the current density. The numerical result is then compared with the flux noise data obtained from YBCO thin films measured with a dc SQUID. Using this method, we can estimate the free energy U0and the bundle size. The invariance of the noise peak position with the detecting coil distance indicates that the configurations of the moving bundles are space invariant so the system is in a self-organized criticality state.