Electron-hole asymmetry in Co- and Mn-dopedSrFe2As2

Abstract

Phase diagrams of electron- and hole-doped ${\text{SrFe}}_{2}{\text{As}}_{2}$ 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 ${\text{SrFe}}_{2\ensuremath{-}x}{\text{Mn}}_{x}{\text{As}}_{2}$. The absence of electron-hole symmetry in the phase diagrams of the Fe-site doped ${\text{SrFe}}_{2}{\text{As}}_{2}$ suggests that the occurrence of high-${T}_{c}$ superconductivity is sensitive to the structural modification rather than the carrier doping.