Fe/Bi superlattices: their crystal and electronic structures

Recent advances in use of high-pressure techniques have enabled a US team to successfully create the first man-made iron-bismuth binary compound, i.e., FeBi₂, at high pressure and temperature. This inspired us to ask whether an Fe/Bi superlattice of proper thickness ratios can exhibit similar physical properties. We thus fabricated by e-beam evaporation the superlattice thin film heterostrcutures of various alternating Fe/Bi bilayer thicknesses. As Fe and Bi are immiscible, the interfaces are expected to be reasonably smooth, though such simple expectation faces uncertainty of crystallographic anisotropy. Some orientations of the bismuth layers would grow more favorably with Fe layers of certain orientations. First-principle calculations were conducted to understand the basic physics underlying structural stabilities and associated electronic structures. The interfaces between the rhombohedral Bi(001) and bcc Fe(001) faces exhibits Moirée pattern from the well-defined periodicity of coincidence-site lattices. The physical properties are understood from systematic comparisons of the bilayer thickness ratios and individual thicknesses per se in accordance both with the theoretical and experimental findings.