Search

The thermal conductivity of iron-based superconductor CsFe2As2 single crystal (Tc=1.81 K) was measured down to 50 mK. A significant residual linear term κ0/T=1.27 mW K-2 cm-1 is observed in zero magnetic field, which is about 1/10 of the normal-state value in upper critical field Hc2. In low magnetic field, κ0/T increases rapidly with field. The normalized κ0/T(H) curve for our CsFe2As2 (with residual resistivity ρ0=1.80 μΩ cm) lies between the dirty KFe2As2 (with ρ0=3.32 μΩ cm) and the clean KFe2As2 (with ρ0=0.21 μΩ cm), which is consistent with its impurity level. These results strongly suggest a nodal superconducting gap in CsFe2As2, similar to its sister compound KFe2As2. [ABSTRACT FROM AUTHOR]

High-quality K(Fe1-xCox)2As2 single crystals have been grown by using the KAs flux method. Instead of increasing the superconducting transition temperature Tc through electron doping, we find that Co impurities rapidly suppress Tc down to zero at only x ≈ 0.04. Such an effective suppression of Tc by impurities is quite different from that observed in Ba0.5K0.5Fe2As2 with multiple nodeless superconducting gaps. Thermal conductivity measurements in zero field show that the residual linear term K0/T only changes slightly with 3.4% Co doping, despite the sharp increase in the scattering rate. The implications of these anomalous impurity effects are discussed. [ABSTRACT FROM AUTHOR]

We measured the resistivity and the specific heat of CsFe2As2 single crystals, which were grown by using a self-flux method. The CsFe2As2 crystal shows a sharp superconducting transition at 1.8 K with a transition width of 0.1 K. The sharp superconducting transition and pronounced jump in specific heat indicate high quality of the crystals. A large ΔCp/Tc accompanying a very low Tc, nonexponential dependence of the lowest temperature ΔCp/ T and an H1/2 dependence of Δγ(H) are observed in the superconducting-state specific heat; Combined with the fitting results by the α model for the superconducting-state specific heat, a pairing symmetry with nodal gaps was suggested in CsFe2As2. [ABSTRACT FROM AUTHOR]