Manifestation of vortex depinning transition in nonlinear current-voltage characteristics of polycrystalline superconductor Y_1-xPr_xBa₂Cu₃O_7-δ

We present our recent results on the temperature dependence of current-voltage characteristics for polycrystalline Y_1-xPr_xBa₂Cu₃O_7-δ superconductors with x = 0.0, 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law of the form V = R (I - I_c)^{a (T)}. Here, we assume that a (T) = 1 + Φ₀ I_C (T) / 2 π k_B T and I_C (T) = I_C (0) (1 - T / T_C)^{3 / 2} for the temperature dependences of the power exponent and critical current, respectively. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current-voltage characteristics curves from Ohmic behavior (with a (T_C) = 1) below T_C is attributed to the manifestation of dissipation processes. They have a characteristic temperature T_p defined via the power exponent as a (T_p) = 2 and are related to the current induced depinning of Abrikosov vortices. Both T_C (x) and T_p (x) are found to decrease with an increase of Pr concentration x reflecting deterioration of the superconducting properties of the doped samples.