I-V characteristic measurements to study the nature of the vortex state and dissipation in MgB₂ thin films

The temperature dependence of current-voltage (I-V) characteristics of MgB₂ thin films has been studied at different magnetic fields (H) and angles (θ) between H and the ab plane. The I-V characteristics obtained at different H and θ show critical scaling indicative of vortex glass transition. The critical exponents are found to be independent of H and θ indicating a universal behavior. The scaling functions are also seen to be field and angle independent when resistivity and current density are normalized with two parameters ρ₀ and J₀, which are functions of H and θ. Field and angle dependences of parameters ρ₀ and J₀, and vortex glass transition temperature T_g are seen to be in agreement with the anisotropic Ginzburg-Landau model.