Superconductivity and phase diagram in Ru-doped SrFe_2xRu_xAs₂ single crystals

Single crystals of SrFe_2xRu_xAs₂ have been successfully synthesized using the FeAs self-flux method. The X-ray diffraction patterns indicate that the substitution of Fe by Ru leads to a decrease of the c parameter. Upon Ru substitution, the resistivity anomaly in the parent compound is progressively suppressed and superconductivity is stabilized at low temperatures for x0.45. The superconducting region is dome-like, with an optimal T_c 15.5K found around x=0.667. A phase diagram of temperature vs. doping, based on electrical transport, has been constructed. Results of upper and lower critical field are presented. Our results confirm that the substitution of Fe ions with isoelectronic Ru could suppress the magnetic/structural phase transition in the parent compound, and suggest that there is strong competition between magnetism, structure, and superconductivity in iron-based superconductors. ©2012