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

We measured the ultra-low-temperature specific heat and thermal conductivity of Au${}_2$Pb single crystal, a possible three-dimensional Dirac semimetal with a superconducting transition temperature $T_c\approx$ 1.05 K. The electronic specific heat can be fitted by a two-band s-wave model, which gives the gap amplitudes ${\mathrm{\Delta }}_1$(0)/$k_B{T}_c$ = 1.38 and ${\mathrm{\Delta }}_2$(0)/$k_B{T}_c$ = 5.25. From the thermal conductivity measurements, a negligible residual linear term ${\kappa }_0\mathrm{/}T$ in zero field and a slow field dependence of ${\kappa }_0\mathrm{/}T$ 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 superconductor if Au${}_2$Pb is indeed one.