Atomic and Electronic Structures in Intermetallic CaBi₂ Thin Films

Bismuth-based alloys and compounds are promising candidates for novel topological nontrivial materials due to the strong spin-orbit coupling effect in the heavy bismuth element. The search for topological superconductivity and Majorana fermions in these materials have attracted significant interest. Recently, intermetallic CaBi₂ single crystal was reported to be superconducting, while the atomic, electronic, and topological properties have never been investigated. Using molecular beam epitaxy, we have successfully grown CaBi₂ thin film on TiO₂-terminated SrTiO₃(100) substrate. The lattice and electronic structures were probed by using in-situ reflection high-energy electron diffraction, scanning tunneling microscopy and ex-situ X-ray diffraction. We found the epitaxial CaBi₂ thin film has a Volmer-Weber growth mode and the surface has four totally different terminations: two are non-reconstructed, and the others are reconstructed to 1×2 and c(5×5), respectively. The different electronic density of states and physical properties relevant to these different surface terminations were also investigated.