Evidence for conventional superconductivity in Bi2PdPt and prediction of possible topological superconductivity in disorder-free γ−BiPd

We present comprehensive investigations into the structural, superconducting, and topological properties of ${\mathrm{Bi}}_{2}\mathrm{PdPt}$. Magnetization and heat-capacity measurements performed on polycrystalline ${\mathrm{Bi}}_{2}\mathrm{PdPt}$ demonstrate a superconducting transition at $\ensuremath{\simeq}$ 0.8 K. Moreover, muon spin relaxation/rotation ($\textmu{}\mathrm{SR}$) measurements present evidence for a time-reversal symmetry preserving, isotropically gapped superconducting state in ${\mathrm{Bi}}_{2}\mathrm{PdPt}$. We have also performed density-functional theory (DFT) calculations on ${\mathrm{Bi}}_{2}\mathrm{PdPt}$ alongside the more general isostructural systems ${\mathrm{BiPd}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x}$, of which ${\mathrm{Bi}}_{2}\mathrm{PdPt}$ and $\ensuremath{\gamma}$-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 nontrivial topological state when $x>0.75$ and a trivial topological state when $x<0.75$. Therefore our results indicate that ${\mathrm{BiPd}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x}$ could be a topological superconductor for $x>0.75$.