Evidence for conventional superconductivity in Bi_2PdPt and prediction of topological superconductivity in disorder-free γ-BiPd

We present comprehensive investigations into the structural, superconducting, and topological properties of Bi_2PdPt. Magnetization and heat capacity measurements performed on polycrystalline Bi_2PdPt 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 Bi_2PdPt. We have also performed density-functional theory (DFT) calculations on Bi_2PdPt alongside the more general isostructural systems, BiPd_xPt_1-x, of which Bi_2PdPt and γ-BiPd are special cases for x=0.5 and x=1 respectively. We have calculated the Z_2 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 non-trivial topological state when x>0.75 and a trivial topological state when x<0.75. Therefore our results indicate that BiPd_xPt_1-x could be a topological superconductor for x>0.75.