Fully gapped superconducting state in Au₂Pb: A natural candidate for topological superconductor

We measured the ultra-low-temperature specific heat and thermal conductivity of the Au₂Pb 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 Δ₁(0)/k _B T _c = 1.41 and Δ₂(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 Au₂Pb has a fully gapped superconducting state in the bulk, which is a necessary condition for topological superconductors if Au₂Pb is indeed one.