Emergent phases of nodeless and nodal superconductivity separated by antiferromagnetic order in iron-based superconductor (Ca4Al2O6)Fe2(As1−xPx)2:75As- and31P-NMR studies

Abstract

We report ${}^{31}$P- and ${}^{75}$As-NMR studies on (Ca${}_{4}$Al${}_{2}$O${}_{6}$)Fe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ with an isovalent substitution of P for As. We present the novel evolution of emergent phases that the nodeless superconductivity (SC) in $0\ensuremath{\le}x\ensuremath{\le}0.4$ and the nodal one around $x=1$ are intimately separated by the onset of a commensurate stripe-type antiferromagnetic (AFM) order in $0.5\ensuremath{\le}x\ensuremath{\le}0.95$, as an isovalent substitution of P for As decreases a pnictogen height ${h}_{Pn}$ measured from the Fe plane. It is demonstrated that the AFM order takes place under a condition of $1.32\phantom{\rule{4pt}{0ex}}\AA{}\ensuremath{\le}{h}_{Pn}\ensuremath{\le}1.42\phantom{\rule{4pt}{0ex}}\AA{}$, which is also the case for other Fe pnictides with the Fe${}^{2+}$ state in (Fe$Pn$)${}^{\ensuremath{-}}$ layers. This novel phase evolution with the variation in ${h}_{Pn}$ points to the importance of electron correlation for the emergence of SC as well as AFM order.