Nodeless superconducting gap in electron-doped BaFe$_{1.9}$Ni$_{0.1}$As$_2$ probed by quasiparticle heat transport

TL;DR

This study investigates the superconducting gap structure of BaFe$_{1.9}$Ni$_{0.1}$As$_2$ using thermal conductivity measurements, revealing a nodeless gap consistent with isotropic gaps on multiple Fermi surface pockets.

Contribution

It provides direct low-temperature thermal conductivity evidence for a nodeless superconducting gap in electron-doped BaFe$_{1.9}$Ni$_{0.1}$As$_2$, supporting previous spectroscopic findings.

Findings

No residual linear term in thermal conductivity at zero field.

Slow field dependence of thermal conductivity up to 30% of $H_{c_2}$.

Consistent with isotropic superconducting gaps observed in ARPES experiments.

Abstract

The in-plane thermal conductivity $\kappa$ of electron-doped iron-arsenide superconductor BaFe$_{1.9}$Ni$_{0.1}$As$_2$ ($T_c$ = 20.3 K) single crystal was measured down to 70 mK. In zero field, the absence of a residual linear term $\kappa_0/T$ at $ T \to 0$ is strong evidence for nodeless superconducting gap. In magnetic field, $\kappa_0/T$ shows a slow field dependence up to $H$ = 14.5 T ($\approx$ 30% $H_{c_2}$). This is consistent with the superconducting gap structure demonstrated by angle-resolved photoemission spectroscopy experiments in BaFe$_{1.85}$Co$_{0.15}$As$_2$ ($T_c$ = 25.5 K), where isotropic superconducting gaps with similar size on hole and electron pockets were observed.