Nodal superconductivity in Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ induced by isovalent Ru substitution

TL;DR

This study reveals that isovalent Ru substitution in BaFe2As2 induces nodal superconductivity, evidenced by heat transport measurements showing residual linear thermal conductivity and field dependence similar to other nodal superconductors.

Contribution

It demonstrates that isovalent Ru substitution can induce nodal superconductivity in BaFe2As2, expanding understanding of how different substitutions affect superconducting gap structures.

Findings

Large residual linear term in thermal conductivity indicates nodes in the superconducting gap.

Field dependence of thermal conductivity follows an H^{1/2} law, consistent with nodal gaps.

Ru substitution induces nodal superconductivity similar to phosphorus substitution.

Abstract

We present the ultra-low-temperature heat transport study of an iron-based superconductor Ba(Fe$_{0.64}$Ru$_{0.36}$)$_2$As$_2$ ($T_c$ = 20.2 K), in which the superconductivity is induced by isovalent Ru substitution. In zero field we find a large residual linear term $\kappa_0/T$, more than 40% of the normal-state value. At low field, the $\kappa_0/T$ shows an $H^{1/2}$ dependence. These provide strong evidences for nodes in the superconducting gap of Ba(Fe$_{0.64}$Ru$_{0.36}$)$_2$As$_2$, which mimics that in another isovalently substituted superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$. Our results show that the isovalent Ru substitution can also induce nodal superconductivity in BaFe$_2$As$_2$, as P does, and they may have the same origin. We further compare them with other two nodal superconductors LaFePO and LiFeP.