Doping dependence of the upper critical field and Hall resistivity ofLaFeAsO1−xFx(x=0, 0.025, 0.05, 0.07, 0.11, and 0.14)

Abstract

The electrical resistivity $({\ensuremath{\rho}}_{xx})$ and Hall resistivity $({\ensuremath{\rho}}_{xy})$ of ${\text{LaFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ have been measured over a wide fluorine-doping range $0\ensuremath{\le}x\ensuremath{\le}0.14$ using 60 T pulsed magnets. While the superconducting phase diagram $({T}_{c},x)$ displays the classic dome-shaped structure, we find that the resistive upper critical field $({H}_{c2})$ increases monotonically with decreasing fluorine concentration, with the largest ${H}_{c2}\ensuremath{\ge}75\text{ }\text{T}$ for $x=0.05$. This is reminiscent of the composition dependence in high-${T}_{c}$ cuprates and might correlate with opening of a pseudogap in the underdoped region. Furthermore, the temperature dependence of ${H}_{c2}(T)$ for superconducting samples can be understood in terms of multiband superconductivity. ${\ensuremath{\rho}}_{xy}$ data for nonsuperconducting samples show nonlinear field dependence, which is also consistent with a multicarrier scenario.