ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$

TL;DR

This study uses ARPES to reveal that Ru-substituted Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ exhibits nearly isotropic superconducting gaps despite Fermi surface warping, supporting the $J_1-J_2$ magnetic interaction model.

Contribution

First ARPES measurement showing isotropic superconducting gaps in Ru-doped BaFe$_2$As$_2$, highlighting the role of magnetic interactions in pairing symmetry.

Findings

Superconducting gaps are nearly isotropic despite Fermi surface warping.

Gaps measured: 5.7 meV and 4.5 meV on hole pockets, 4.8 meV on electron pockets.

Results support the $J_1-J_2$ model with dominant antiferromagnetic exchange.

Abstract

We used high-energy resolution angle-resolved photoemission spectroscopy to extract the momentum dependence of the superconducting gap of Ru-substituted Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ ($T_c = 15$ K). Despite a strong out-of-plane warping of the Fermi surface, the magnitude of the superconducting gap observed experimentally is nearly isotropic and independent of the out-of-plane momentum. More precisely, we respectively observed 5.7 meV and 4.5 meV superconducting gaps on the inner and outer $\Gamma$-centered hole Fermi surface pockets, whereas a 4.8 meV gap is recorded on the M-centered electron Fermi surface pockets. Our results are consistent with the $J_1-J_2$ model with a dominant antiferromagnetic exchange interaction between the next-nearest Fe neighbors.