Robust Nodal Superconductivity Induced by Isovalent Doping in Ba(Fe_{1-x}Ru_{x})_{2}As_{2} and BaFe_{2}(As_{1-x}P_{x})_{2}

Abstract

We present the ultra-low-temperature heat-transport study of iron-based superconductors Ba(Fe_{1-x}Ru_{x})_{2}As_{2} and BaFe_{2}(As_{1-x}P_{x})_{2}. For optimally doped Ba(Fe_{0.64}Ru_{0.36})_{2}As_{2}, a large residual κ_{0}/T at zero field and a sqrt[H] dependence of κ_{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(Fe_{0.64}Ru_{0.36})_{2}As_{2} may have the same origin as in BaFe_{2}(As_{0.67}P_{0.33})_{2}. Furthermore, in underdoped Ba(Fe_{0.77}Ru_{0.23})_{2}As_{2} and strongly underdoped BaFe_{2}(As_{0.82}P_{0.18})_{2}, κ_{0}/T manifests similar nodal behavior, which result shows the robustness of nodal superconductivity in the underdoped regime and puts constraint on theoretical models.