Prediction of two-dimensional topological insulator by forming surface alloy on Au/Si(111) substrate

Two-dimensional (2D) topological insulators (TIs), which can be integrated into the modern silicon industry, are highly desirable for spintronics applications. Here, using first-principles electronic structure calculations, we show that the Au/Si(111)-root3 substrate can provide a new platform for hosting 2D-TIs obtained through the formation of surface alloys with a honeycomb pattern of adsorbed atoms. We systematically examined elements from groups III to VI of the periodic table at 2/3 monolayer coverage on Au/Si(111)-root3, and found that In, Tl, Ge, and Sn adsorbates result in topologically non-trivial phases with band gaps varying from zero to 72 meV. Our scanning tunneling microscopy and low-energy electron diffraction experiments confirm the presence of the honeycomb pattern when Bi atoms are deposited on Au/Si(111)-root3 in accord with our theoretical predictions. Our findings pave the way for using surface alloys as a potential new route for obtaining viable 2D-TI platforms.