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

Abstract

We present comprehensive investigations into the structural, superconducting, and topological properties of Bi2⁢PdPt. Magnetization and heat-capacity measurements performed on polycrystalline Bi2⁢PdPt demonstrate a superconducting transition at ≃ 0.8 K. Moreover, muon spin relaxation/rotation (µ⁢SR) measurements present evidence for a time-reversal symmetry preserving, isotropically gapped superconducting state in Bi2⁢PdPt. We have also performed density-functional theory (DFT) calculations on Bi2⁢PdPt alongside the more general isostructural systems BiPd𝑥⁢Pt1−𝑥, of which Bi2⁢PdPt 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 BiPd𝑥⁢Pt1−𝑥 could be a topological superconductor for 𝑥>0.75.