Electron-hole asymmetry in Co- and Mn-doped SrFe2As2

Phase diagrams of electron- and hole-doped SrFe2As2 single crystals are investigated using Co and Mn substitution at the Fe sites. We find that the spin-density-wave state is suppressed by both dopants but the superconducting phase appears only for Co (electron) doping, not for Mn (hole) doping. Absence of the superconductivity by Mn doping is in sharp contrast to the hole-doped system with K substitution at the Sr sites. First-principles calculations based on detailed structural investigations reveal that a distinct structural change, i.e., the increase in the Fe-As distance by Mn doping is the most decisive factor to induce a magnetic and semiconducting ground state in SrFe2-xMnxAs2. The absence of electron-hole symmetry in the phase diagrams of the Fe-site doped SrFe2As2 suggests that the occurrence of high-T-c superconductivity is sensitive to the structural modification rather than the carrier doping.