Superconductivity at 25 K in hole-doped (La 1-x Sr x )OFeAs

By partially substituting the tri-valence element La with di-valence element Sr in LaOFeAs, we introduced holes into the system. For the first time, we successfully synthesized the hole-doped new superconductors (La 1- x Sr x )OFeAs. The maximum superconducting transition temperature at about 25 K was observed at a doping level of x =0.13. It is evidenced by Hall effect measurements that the conduction in this type of material is dominated by hole-like charge carriers, rather than electron-like ones. Together with the data of the electron-doped system La(O 1- x F x )FeAs, a generic phase diagram is depicted and is revealed to be similar to that of the cuprate superconductors.