To gain insight into the unconventional superconductivity of Fe pnictides with no electron pockets, we measure the thermal conductivity κ and penetration depth λ in the heavily hole-doped regime of Ba1-xKxFe2As2. The residual thermal conductivity (κ/T)T→0K and T dependence of λ consistently indicate the fully gapped superconductivity at x=0.76 and the (line) nodal superconductivity at higher hole concentrations. The magnitude of κTTc|T→0K and the slope of λ(T) at low temperatures, both of which are determined by the properties of the low-energy excitations, exhibit a highly unusual nonmonotonic x dependence. These results indicate a dramatic change of the nodal characteristics in a narrow doping range. We suggest that the observed x dependence is naturally explained by a doping crossover of the gap function between the s-wave states with and without sign reversal between Γ-centered hole pockets.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Mar 11 2014|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics