Robust Nodal Superconductivity Induced by Isovalent Doping in Ba(Fe1-xRux)(2)As-2 and BaFe2(As1-xPx)(2)

Abstract

We present the ultra-low-temperature heat-transport study of iron-based superconductors Ba(Fe1-xRux)(2)As-2 and BaFe2(As1-xPx)(2). For optimally doped Ba(Fe0.64Ru0.36)(2)As-2, a large residual kappa(0)/T at zero field and a root H dependence of kappa(0)(H)/T are observed, which provide strong evidences for nodes in the superconducting gap. This result demonstrates one more nodal superconductor in iron pnictides. The similarities between isovalent Fe and P dopings strongly suggest that the nodal superconductivity in Ba(Fe0.64Ru0.36)(2)As-2 may have the same origin as in BaFe2(As0.67P0.33)(2). Furthermore, in underdoped Ba(Fe0.77Ru0.23)(2)As-2 and strongly underdoped BaFe2(As0.82P0.18)(2), kappa(0)/T manifests similar nodal behavior, which result shows the robustness of nodal superconductivity in the underdoped regime and puts constraint on theoretical models.