Model for the broadening of the resistive transition in YBa2Cu3O7-δ thin films

A new analysis of the broadening of the resistive transition under magnetic field in YBa₂Cu₃O_7-δ thin films is presented, providing a very good description of the ρ(T) behaviour up to 50% of the normal state resistivity, for fields up to 18 T. We describe films as a collection of clean regions which present a sharp resistivity drop, as observed in clean single crystals and attributed to the vortex lattice melting transition. The structural or chemical inhomogeneities existing in films are modelled by a distributed melting temperature. The field dependence of the distribution width is coherently described by our model. This model, using the classical flux flow theory, yields values for dB_c2/dT and for the vortex viscosity in close agreement with those currently accepted.