Heavy Electron doping-induced antiferromagnetic phase as the parent for   iron-oxypnictide superconductor LaFeAsO1-xHx
  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. 
Soshi Iimura, Satoru Matsuishi, and Hideo Hosono
cond-mat.supr-con