Ground states of Au2Pb and pressure-enhanced superconductivity

Abstract

$\mathrm{A}{\mathrm{u}}_{2}\mathrm{Pb}$ is a candidate of natural topological superconductors that has attracted much attention in the last few years. Combining ab initio calculations with machine-learning accelerated crystal structure searches, we have found two ground states of $\mathrm{A}{\mathrm{u}}_{2}\mathrm{Pb}$: $Pca{2}_{1}$ phase at ambient pressure and $I\overline{4}2d$ phase at high pressure. The $Pca{2}_{1}$ phase is energetically more favorable than the known Pbcn structure and can be a candidate for x-ray diffraction refinement; our calculations suggest that high-pressure $I\overline{4}2d$ is a conventional superconductor. By the high-pressure electric resistance measurements, we observed evidence of a ${T}_{c}$ enhancement. ${T}_{c}$ reaches a maximum value of around 4 K at 5 GPa, then decreases with further compression. The superconductivity can remain unchanged after pressure releasing, in line with our theoretical predictions. These results show that $\mathrm{A}{\mathrm{u}}_{2}\mathrm{Pb}$ exhibits abundant behaviors under varied pressure and temperature, which can help to understand how to adjust its electronic properties by pressure.