Ground states of Au2Pb and pressure-enhanced superconductivity

Au2Pb 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 Au2Pb: Pca2(1) phase at ambient pressure and I (4) over bar 2d phase at high pressure. The Pca2(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 (4) over bar 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 Au2Pb exhibits abundant behaviors under varied pressure and temperature, which can help to understand how to adjust its electronic properties by pressure.