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

Abstract

-We measured the ultra-low-temperature specific heat and thermal conductivity of Au2Pb single crystal, a possible three-dimensional Dirac semimetal with a superconducting transition temperature Tc ≈ 1.05 K. The electronic specific heat can be fitted by a two-band s-wave model, which gives the gap amplitudes ∆1(0)/kBTc = 1.38 and ∆2(0)/kBTc = 5.25. From the thermal conductivity measurements, a negligible residual linear term κ0/T in zero field and a slow field dependence of κ0/T 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 superconductor if Au2Pb is indeed one.

Emergence of Topological Superconductivity in Doped Topological Dirac Semimetals under Symmetry-Lowering Lattice Distortions

“…Now, we compare our results with experimental works in doped DSM of Au 2 Pb [30][31][32][33][34] and Cd 3 As 2 [27][28][29] . Au 2 Pb shows superconductivity at T c ≈ 1.2K with D 2h symmetry at the ambient pressure 30,32,34 .…”

“…For both materials, the point-contact measurements reported that measured T c using a hard contact tip is much higher than the measured T c using a soft tip 27,29,32 . The point-contact measurements for Cd 3 As 2 showed the zero-bias conductance peak (ZBCP) and double conductance peaks symmetric around zero bias, which was interpreted as a signal of a topological Majorana surface superconductivity is reported in Cd 3 As 2 [27][28][29] and Au 2 Pb [30][31][32][33][34] . Both materials have Dirac points protected by TRS, IS, and C 4 rotational symmetry and share the tetragonal crystal system with D 4h point group symmetry.…”

“…In the absence of lattice distortions, Cd 3 As 2 [27][28][29] and Au 2 Pb [32][33][34] share the same D 4h point group symmetry and show no superconductivity. However, both materials showed superconductivity after the structural phase transition under pressure or cooling, and the superconducting critical temperature increases with the pressure 28,34 .…”

“…Recently, the lattice-distortion induced superconductivity in DSMs of Cd 3 As 2 [27][28][29] and Au 2 Pb [30][31][32][33][34] is reported. For Cd 3 As 2 , it does not show any superconductivity at the ambient pressure until 1.8 K [27][28][29] .…”

Emergence of topological superconductivity in doped topological Dirac semimetals under symmetry-lowering lattice distortions

“…5 ). The experiments reported that the superconductivity is either conventional 33 , 34 or unconventional 32 depending on the physical situations. From our analysis, the superconducting phase of Pb is expected to be either a conventional fully gapped or unconventional topological mirror superconductor with a gapless SABS depending on physical parameters.…”