Doping dependence of the upper critical field of electron-doped Pr2-xCexCuO4 thin films -: art. no. 094507

Using resistivity measurements as a function of applied magnetic field down to 38 mK, we evaluate the temperature dependence of the c-axis upper critical field (H-c2,H-rho) for electron-doped Pr2-xCexCuO4 thin films. We compare its temperature dependence to the irreversibility line as determined by ac susceptibility [H-IL(T)] between 2 K and the transition temperature. For all Ce contents, H-c2,H-rho(T) presents an upward curvature, with no sign of the expected conventional saturation at low temperature, even down to 38 mK. The onset of resistivity follows closely the irreversibility line, and the general trend in temperature for H-c2,H-rho(T) is rather insensitive to the criterion used for its determination. Only a rough criterion corresponding to a full recovery of the normal-state resistivity for x=0.15 is bringing the characteristic field temperature dependence close to the expected description by Werthamer, Helfand and Hohenberg. Doping affects mainly the zero-temperature value of H-c2,H-rho and H-IL which are scaling with the critical temperature, but not the superconducting gap. The temperature dependence is very similar to that observed with the hole-doped cuprates, and underlines a similar physical origin related to the properties in the vortex-liquid phase and contributions of superconducting fluctuations.