First-principles study of light-element doping effects on iron-based superconductors

Since the discovery of the iron-based superconductor, LaFeAsO$_{1-x}$F$_x$ whose Tc reached 26K, various types of iron-based superconductors have been fabricated to attain higher $T_c$. Recently, it is reported that Tc of an iron-based superconductor LaFeAsO$_{1-y}$ is enhanced to 35K by doping hydrogen. This result implies that atoms of light elements penetrate into the crystal of iron-based superconductors and transform their structures into more useful ones for superconductivity. In this talk, we investigate how the light elements are doped in the iron-based superconductors by using the first-principles density functional theory. Furthermore, we evaluate the effects of doping on the crystal structures and electronic states and explore the origin of the $T_c$ enhancements.