Surface alloy engineering in 2D trigonal lattice: giant Rashba spin splitting and two large topological gaps

We demonstrate that sp 2 based trigonal lattice can exhibit giant Rashba splitting and two large topological gaps simultaneously. First, an effective tight binding model is developed to describe the Rashba spin–orbit coupling (SOC) on a real surface and give a topological phase diagram based on two independent SOC parameters. Second, based on density functional theory calculations, it is proposed that Au/Si(111)- surface with 1/3 monolayer Bi coverage is a good material candidate to realize both giant Rashba splitting and two large topological gaps. These results would inspire great research interests for searching two-dimensional topological insulator and manipulating Rashba spin splitting through surface alloy engineering.