Pinning, creep and possible melting in the mixed state of NbZr films

Abstract

Current-Voltage (I-V) characteristics and resistivity measurements on Nb_xZr_1-x (x~ 0.15) thin films are reported over a broad range of temperature and magnetic field. In the vicinity of the critical temperature (field) the I-V curves show a transition from the Ohmic to a strongly non-linear behavior on increasing the excitation current density. The linear resistivity is thermally activated with a field dependent barrier height. Although the Ohmic and non-linear data can be described in the framework of the glass model for the mixed state in hard superconductors, it does not yield a universal set of exponents for the glass to fluid transition. The overall response of the mixed state can be understood in the framework of the standard flux-creep theory with inter-vortex interaction.