Hydrogen in layered iron arsenides; Indirect electron doping to induce superconductivity

Hanna, Taku*; Muraba, Yoshinori*; Matsuishi, Satoru*; Igawa, Naoki   ; Kodama, Katsuaki   ; Shamoto, Shinichi  ; Hosono, Hideo*

Utilizing the high stability of calcium and rare-earth hydrides, CaFeAsFH ( = 0.0-1.0) and SmFeAsOH ( = 0.0-0.47) have been synthesized using high pressure to form hydrogen-substituted 1111-type iron-arsenide superconductors. Neutron diffraction and density functional calculations have demonstrated that the hydrogens are incorporated as H ions occupying F sites in the blocking layer of CaFeAsF. The resulting CaFeAsOH is nonsuperconducting, whereas, SmFeAsOH is a superconductor, with an optimal =55 K at 0.2. It was found that up to 40% of the O ions can be replaced by H ions, with electrons being supplied into the FeAs layer to maintain neutrality (O = H + e). When exceeded 0.2, was reduced corresponding to an electron overdoped region.