Spectral distribution of activation energies in YBa2Cu3O7-δ thin films

Local magnetic relaxation experiments are carried out on YBa2Cu3O7-delta thin films by magneto-optics. The current density is calculated quantitatively by an inversion scheme of Blot Savart's law which gives direct information about the time evolution of the current density with a high spatial resolution of about 5 mum. We determine the local activation energies U-0(x,y) by fitting different relaxation laws at different positions (x, y) in the film plane. This analysis yields a spectral distribution of the activation energies that is independent of the applied model. Possible mechanisms which could lead to such a distribution are discussed.