Superconductivity in Hole-Doped (Sr 1−x K x )Fe ₂ As ₂

A series of layered (Sr 1-x K x )Fe 2 As 2 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 SrFe 2 As 2 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 BaFe 2 As 2 , the two prototype parent compounds with ZrCuSiAs- and ThCr 2 Si 2 -type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe 2 As 2 , sharp superconducting transitions at T c ∼ 38 K 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.