Atomic Structure and Electronic Properties of Intermetallic CaBi₂ Thin Films

Intermetallic bismuth-based compounds have attracted great interest as promising candidates for novel topological superconductivity. Among them, CaBi₂ is a newly discovered member for which the atomic structure and electronic properties have never been systematically explored. Using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we systematically characterized the atomic structure and electronic properties of CaBi₂(010) thin films grown by molecular beam epitaxy (MBE) and found that their growth follows a Stranski-Krastanov mode. A nonreconstructed I_Bi layer and a (1 × 2) reconstructed II_Ca layer were found to be the most common surfaces. Nonreconstructed III_Bi and V_Ca layers were further exposed with reduced bismuth growth flux. All of these constituent layers exhibit unique features in the STS spectra, indicating that unique electronic properties exist in each specific constituent layer. Our findings provide for deeper understanding of the physical properties of this compound and suggest further studies of the two-dimensional (2D) layered materials family.