Superconductivity at 48 K of heavily hydrogen-doped SmFeAsO epitaxial films grown by topotactic chemical reaction using CaH2

High critical-temperature (Tc) superconductivity at 48 K is reported for hydrogen-doped SmFeAsO epitaxial films on MgO single-crystal substrates. The key processes are pulsed laser deposition to grow undoped SmFeAsO epitaxial films and subsequent topotactic chemical reaction using CaH2 powders under evacuated silica-glass ampule atmosphere. This post-deposition thermal annealing treatment we have developed realizes maximum hydrogen concentration x = ~0.35 in SmFeAs(O1-xHx). Disordered hydrogen-substitution at O sites is experimentally confirmed directly by atomic-scale microstructure observation. Complete diamagnetism in magnetization measurements validates the bulk nature of the high-Tc superconductivity in the films. This method will become an effective and general method to fabricate various high-quality oxyhydride epitaxial films.