Stability of topological properties of bismuth (111) bilayer

We investigate electronic and transport properties of bismuth (111) bilayer in the context of stability of its topological properties against different perturbations. The effects of spin-orbit coupling variations, geometry relaxation and an interaction with a substrate are considered. Transport properties are studied in the presence of Anderson disorder. Band structure calculations are performed within multi-orbital tight-binding model and density functional theory methods. A band inversion process in bismuth (111) infinite bilayer and an evolution of edge states dispersion in ribbons as a function of spin-orbit coupling strength are analyzed. A significant change of orbital composition of the conduction and valence bands during a topological phase transition is observed. A topological phase is shown to be robust when the effect of geometry relaxation is taken into account. An interaction with a substrate has similar effect to an external perpendicular electric field. The robust quantized conductance is observed when the Fermi energy lies within the bulk energy gap, where only two counter-propagating edge states are present. For energies where the Fermi level crosses more in-gap states, a scattering is possible between channels lying close in $k-$space. When the energy of edge states overlaps with bulk states, no topological protection is observed.