Superconducting properties of Bi₂PdPt and prediction of topological superconductivity in the disorder-free limit

Bismuth-containing superconducting alloys have attracted a lot of research interest in the last decade due to their topologically non-trivial band structures and unconventional superconducting properties [1-2]. In this talk, I will discuss the structural and physical properties along with density functional theory (DFT) calculations for Bi₂Pd_xPt_1-x. Our zero field-(muon spin relaxation/rotation) μSR measurements of superconducting Bi₂PdPt present evidence for a time reversal symmetry preserving superconducting state. Furthermore, our transverse field μSR measurements of the penetration depth as a function of temperatures suggest an isotropic, fully-gapped superconducting state.

We have calculated the Z₂ topological index from our DFT calculations for Bi₂Pd_xPt_1-x, between x=0 and x=1. Our findings reveal non-trivial topological state (Z₂=1) when x>0.75 and a trivial topological state (Z₂=0) when x<0.75. This shows that γ-BiPd is topologically non-trivial and Bi₂PdPt (x=0.5) is topologically trivial but is close to the critical substitution fraction of x=0.75 predicted in DFT.

[1] Sun, Z., Enayat, M., Maldonado, A. et al. Nat Commun 6, 6633 (2015).

[2] Hyunsoo Kim et al., Sci. Adv.4,eaao4513(2018)