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

Abstract

The in-plane thermal conductivity $\hat{I}º$ 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 $\hat{I}{º}_0/T$ at $T\to 0$ is strong evidence for nodeless superconducting gap. In magnetic field, $\hat{I}{º}_0/T$ 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.

In-field data re-measured with sample cooled in magnetic field from above Tc