Abstract and subjects
We have performed low-temperature specific heat C and thermal conductivity kappa measurements on the Ni-pnictide superconductors BaNi2As2 (T-c = 0.7 K) and SrNi2P2 (T-c = 1.4 K). The temperature dependences C(T) and kappa(T) of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual kappa for BaNi2As2 rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba0.6La0.4Ni2As2 shows a mild suppression of T-c and H-c2 relative to BaNi2As2.