Nodeless superconducting gap in electron-doped BaFe1.9Ni0.1As2 probed by quasiparticle heat transport

The in-plane thermal conductivity kappa of electron-doped iron-arsenide superconductor BaFe1.9Ni0.1As2 (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 -> 0 is strong evidence for a nodeless superconducting gap. In magnetic field, kappa(0)/T shows a slow field dependence up to H = 14.5 T (approximate to 30% H-c2). This is consistent with the superconducting gap structure demonstrated by angle-resolved photoemission spectroscopy experiments in BaFe1.85Co0.15As2 (T-c = 25.5 K), where isotropic superconducting gaps with similar size on hole and electron pockets were observed.