Doping dependence of the upper critical field and Hall resistivity of LaFeAsO1-x Fx (x=0, 0.025, 0.05, 0.07, 0.11, and 0.14)

The electrical resistivity (ρxx) and Hall resistivity (ρxy) of LaFeAsO1-x Fx have been measured over a wide fluorine-doping range 0≤x≤0.14 using 60 T pulsed magnets. While the superconducting phase diagram (Tc, x) displays the classic dome-shaped structure, we find that the resistive upper critical field (Hc2) increases monotonically with decreasing fluorine concentration, with the largest Hc2 75 T for x=0.05. This is reminiscent of the composition dependence in high- Tc cuprates and might correlate with opening of a pseudogap in the underdoped region. Furthermore, the temperature dependence of Hc2 (T) for superconducting samples can be understood in terms of multiband superconductivity. ρxy data for nonsuperconducting samples show nonlinear field dependence, which is also consistent with a multicarrier scenario.