Heavy electron doping induced antiferromagnetic phase as the parent for the iron oxypnictide superconductorLaFeAsO1−xHx

Abstract

We perform transport measurements and band structure calculations of electron-doped LaFeAsO1-xHx over a wide range of x from 0.01 to 0.66. The T^2 and sqrt(T) dependency of the resistivity are observed at x ~ 0.17 and 0.41, respectively. The sign change of RH without opening of the spin-density-wave gap for 0.45 < x < 0.58 and T < TN as well as the calculated non-nested Fermi surface at x = 0.5 indicate the more localized nature of the AF2 as compared to spin density wave phase at non-doped sample. Considering the results from band calculations and the finite size of Hund' s rule coupling, the change of the normal conducting state with x is reasonably explained by a strong depression of the coherent scale owing to the increased effective Coulomb repulsion in the narrow anti-bonding 3dxy band that approaches the half-filled regime. The following transition from the paramagnet to AF2 is understood as the quenching or ordering of the less-screened spins with a large entropy at low temperature. These results suggest that the normal conducting properties over a wide doping range for the LaFeAsO1-xHx are strongly influenced by the local spins in the incoherent region. Thus, we conclude that the parent phase in LaFeAsO1-xHx is not the spin-density wave but the AF2, which may be primarily responsible for the singular superconducting properties of the 1111 type compared with other iron pnictides.