Fully gapped superconducting state in Au 2 Pb: A natural candidate for topological superconductor

We measured the ultra-low-temperature specific heat and thermal conductivity of the Au 2 Pb single crystal, a possible three-dimensional Dirac semimetal with a superconducting transition temperature . The electronic specific heat can be fitted by a two-band s -wave model, which gives the gap amplitudes Δ 1 (0)/ k B T c = 1.41 and Δ 2 (0)/ k B T c = 5.25. From the thermal conductivity measurements, a negligible residual linear term in zero field and a slow field dependence of at low field are obtained. These results suggest that Au 2 Pb has a fully gapped superconducting state in the bulk, which is a necessary condition for topological superconductors if Au 2 Pb is indeed one.