Direct response of the spin-density wave transition and superconductivity to anion height in SrFe2As2

We explored the effects of isovalent doping on the evolution of structure, spin-density wave (SDW), and superconductivity (SC) in three series of Ba-doped SrFe2As2-yPy (y=0.5,0.7,1.0). For the y=0.5 series, the SDW and SC can coexist in the all-Ba-doped SrFe2As1.5P0.5, while the SC first decreases and then saturates in the case of y=0.7. Besides, it is strikingly found that the SC of Ba-doped SrFe2AsP exhibits a dome-shaped Tc, in which the anion height, hpn, approaching the optimal value of 1.308(2) Å and the Tc simultaneously increase to the maxima. The phase diagrams of SDW and SC as a function of hpn and Pn-Fe-Pn angle are first constructed here. It is argued that the isovalent substitutions in FeAs-based superconductors could significantly alter SC and ground states equally as well as carrier doping. The theoretical calculations show that electronic band structure is strongly dependent on the parameter of hpn without introducing carriers by doping. The transition from three-dimensional-like to two-dimensional electronic states and the nesting of the Fermi surface can be realized by changing the hpn.