Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies
Abstract
We report 31P- and 75As-NMR studies on (Ca4Al2O6)Fe2(As1-xPx)2 with an isovalent substitution of P for As. We present the novel evolution of emergent phases that the nodeless superconductivity (SC) in 0 x 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 x 0.95, as an isovalent substitution of P for As decreases a pnictogen height hPn measured from the Fe plane. It is demonstrated that the AFM order takes place under a condition of 1.32 hPn 1.42, which is also the case for other Fe-pnictides with the Fe2+ state in (FePn)- layers. This novel phase evolution with the variation in hPn points to the importance of electron correlation for the emergence of SC as well as AFM order.