Superconductors in the PtPb3Bi Structure Type

Abstract

The quest for new superconductors is of both fundamental and technological importance. Recently, an artificial intelligence method correctly predicted PtPb3Bi to be a superconductor. In this work, we find superconductivity in the newly synthesized MPb4–xBix (M = Au, Pd, and Rh), of which PtPb3Bi is a member. When M = Ni, whose radius is considerably smaller, the structure instead collapses into the different Pb-substituted NiBi3 type. Interestingly, the stoichiometric parameter x shifts across the three compounds to keep the total valence-electron count close to 20 per formula unit. The superconducting transitions occur at 4.9, 4.2, and 3.4 K, for M = Au, Pd, and Rh, respectively. Using electrical resistivity, magnetization, and specific heat measurements, we establish the bulk nature of the superconducting state and determine the critical fields, characteristic length scales, and anisotropy ratios. All three compounds are moderately anisotropic conventional type-II superconductors, with modest upper critical field anisotropies of Hc2∥c/Hc2⊥c ≈ 1.2 to 1.5. These results establish MPb4–xBix as a family of anisotropic superconductors and a platform for studying how site disorder and Pb–Bi mixing govern superconductivity in heavy-element intermetallics.