First-principles study of atomic structures and electronic properties of ultrathin Bi films on Ge(111)

摘要

The atomic and electronic structures of ultrathin bismuth films on Ge(111) surface were investigated using first-principles calculations at Bi coverages ranging from 1/3 ML to 5 ML. Morphology of the surfaces varied as the coverage of Bi was increased. The first layer of bismuth atoms followed the well-known trimer model, exhibiting large Rashba spin-splittings. At 2 ML, bismuth atoms of the second monolayer form the second stacking layer of trimers, whereas at 3 ML and 5 ML, bismuth atoms of the two topmost monolayers form a buckled honeycomb structure. While the electronic structures of the two topmost layers exhibit two-dimensional nontrivial topological insulating phase, the bismuth atoms lying under these layers play an important role in p-type doping of the system.