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

Wedemonstrate that sp based trigonal lattice can exhibit giant Rashba splitting and two large topological gaps simultaneously. First, an effective tight bindingmodel is developed to describe the Rashba spin–orbit coupling (SOC) on a real surface and give a topological phase diagrambased on two independent SOCparameters. Second, based on density functional theory calculations, it is proposed that Au/Si(111) ́ 3 3 surface with 1/3monolayer Bi coverage is a goodmaterial 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 andmanipulating Rashba spin splitting through surface alloy engineering.