Multiple-Pseudogap Phases In The Hydrogen-Doped Lafeaso System

The low-energy electronic structure of LaFeAsO1-x H-x (0.0 <= x <= 0.60), a system which exhibits two superconducting domes and antiferromagnetic orders in its phase diagram, is investigated by utilizing laser photoemission spectroscopy. From the precise temperature-dependent measurement of the spectra near the Fermi level, we find a suppression of the density of states with cooling, namely a pseudogap formation, for all doping range. The pseudogap gets suppressed on doping through the first superconducting dome regime to the higher-x region, whereas it tends to recover when further increasing x toward the second antiferromagnetic ordered phase. The systematic doping dependence indicates the different origins of pseudogaps in the low-and high-x regions, possibly related to the respective antiferromagnetic ground states residing at both ends of the phase diagram.