Critical and Gaussian conductivity fluctuations in a BaFe1.9Ni0.1As2 superconductor

We study fluctuation conductivity in a single crystal of BaFe1.9Ni0.1As2 superconductor (T-c = 20 K) as a function of temperature and applied magnetic field. Magneto-conductivity curves, Delta sigma versus T, were analyzed in terms of -1/(d ln(Delta sigma)/dT) versus T plots, which allow us to study different fluctuation regimes and to estimate exponent values and temperature widths of each regime. The analysis of magneto-conductivity curves evidences the existence of only two fluctuation regimes, a possible critical one (of glass-like type) going from the irreversible temperature to above T-c(H), followed by Aslamazov-Larkin fluctuations in the Gaussian regime.