Fluctuation conductance and critical fields of thin films of NdCeCuO

We describe transport properties at low temperatures and in high magnetic fields of thin films of Nd1.85Ce0.15CuO4-δ, prepared by the process of laser ablation. Above Tc, which is close to 20 K, the effects of superconducting conductance fluctuations are revealed by a positive magnetoresistance. The form of the fluctuations is fitted to the Aslamazov-Larkin and Maki-Thompson expressions in two dimensions. Below Tc, in fields above the upper critical field Hc2, fluctuations are also observed and are used to extract the position of Hc2 in the broad and featureless resistive transition. In contrast to critical field curves obtained by a constant R/Rn criterion, the temperature dependence extracted by this method follows the conventional Werthamer-Helfand-Hohenberg theory, except close to Tc. © 1992.