Effect of transport currents on the critical state of YBa2Cu3O7-δ thin films

After preparation of the remanent critical state, the normal component of the local time-dependent magnet field Bz near the surface of a YBa2Cu3O7-δ thin film was measured before, during, and after the application of a transport current. The results are shown to be consistent with new calculations of Bz for the thin film geometry. The calculated behavior in a thin film is shown to be substantially different from that of the Bean critical state in a long slab in a parallel field. In slab geometry, starting from the remanent critical state, |J(x)| is always equal to Jc, whereas in thin films a continuous distribution of current densities J(x) is found. This feature results in a unique distribution of the magnetic field Bz and unusual magnetic relaxation behavior in the presence of a transport current