Superconductivity in Hole-Doped (Sr_1-xK_x)Fe₂As₂

A series of layered (Sr_1-xK_x)Fe₂As₂ compounds with nominal x=0--0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe₂As₂ shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe₂As₂, the two prototype parent compounds with ZrCuSiAs- and ThCr₂Si₂-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe₂As₂, sharp superconducting transitions at T_c38K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.