DETERMINATION OF THE UPPER CRITICAL-FIELD OF THE ELECTRON-DOPED SUPERCONDUCTOR SM1.85CE0.15CUO4-Y FROM RESISTIVE FLUCTUATIONS

The upper critical field H(c2)(T) for the magnetic field applied parallel to the c axis of a Sm1.85Ce0.15CuO4-y Single crystal has been determined from an analysis of magnetoresistance data in terms of the Ginzburg-Landau fluctuation theory for layered superconductors. The fluctuations are predominantly two dimensions (2D) away from T(c)(H) with a crossover to 3D as T(c)(H) is approached. The H(c2)(T) curve shows negative curvature and is in excellent agreement with the Werthamer, Helfand, Hohenberg, and Maki theory for conventional superconductors without paramagnetic limiting effects. The values of the initial slope (dH(c2)/dT)T(c) = -7.38 kOe/K, coherence length xi(0) = 48.4 angstrom, and orbital critical field H(c2)(0) =97.6 kOe, derived from this analysis, are in good agreement with the values we previously obtained from fits of the Hao-Clem variational model to reversible magnetization data below T(c).