Evidence for conventional superconductivity in Bi2 PdPt and prediction of possible topological superconductivity in disorder-free γ-BiPd

We present comprehensive investigations into the structural, superconducting, and topological properties of Bi2PdPt. Magnetization and heat-capacity measurements performed on polycrystalline Bi2PdPt demonstrate a superconducting transition at ≃ 0.8 K. Moreover, muon spin relaxation/rotation (μSR) measurements present evidence for a time-reversal symmetry preserving, isotropically gapped superconducting state in Bi2PdPt. We have also performed density-functional theory (DFT) calculations on Bi2PdPt alongside the more general isostructural systems BiPdxPt1-x, of which Bi2PdPt and γ-BiPd are special cases for x=0.5 and x=1, respectively. We have calculated the Z2 topological index from our DFT calculations for a range of substitution fractions x, between x=0 and x=1, characterizing the topology of the band structure. We find a nontrivial topological state when x>0.75 and a trivial topological state when x<0.75. Therefore our results indicate that BiPdxPt1-x could be a topological superconductor for x>0.75.