Bi/Ge(111): A first-principles study*

In a separate study, we have shown that a hole-doped Pb₃Bi monolayer can serve as a highly appealing new platform for realizing two-dimensional (2D) intrinsic chiral topological superconductivity. Using first-principles calculations, here we systematically investigate the structural stability of Pb₃Bi grown on Ge(111) substrate, and find two nearly degenerate lattice configurations labeled as T₁ and H₃. For the T₁ structure, the appearance of type-II van Hove singularity in the density of states arises from the Bi doping, where the p orbit of Bi hybridizes with that of Pb, leading to the emergence of saddle-like band structures. Moreover, for both the T₁ and H₃ structures, Bi doping gives rise to larger Rashba-type splittings of the energy bands. We also find a sizable energy barrier of ~0.30 eV per formula unit from the T₁ to H₃ structure. These findings are expected to stimulate new research activities in searching for 2D intrinsic topological superconductors.