La-Substituted CaFeAsH Superconductor with T_c = 47 K

摘要

La-substituted CaFeAsH, (Ca_(1-x)La_x)FeAsH, were synthesized by the solid state reaction at 1173 K under high pressure of 2.5 GPa. The ρ-T anomaly corresponding to tetragonal to orthorhombic structural transition was suppressed by La-substitution and then the superconductivity was observed at an electron doping content of N_e > 0.05. The maximum onset T_c of 47.4 K was reached for N_e = 0.18, which is significant increase compared to 23 K achieved by direct electron doping to the FeAs-layer via Co-substitution to the Fe-site. This value of T_c value fits well to the phenomenological relation between T_c and the bond angle of As-Fe-As in indirectly electron doped LnFeAsO (Ln = Lanthanide). These results indicate that the electron was doped via the indirect mode through the aliovalent ion substitution to CaH-layer （Ca~(2+) → La~(3+) + e~-）.