Interface orbital engineering of large-gap topological states: Decorating gold on a Si(111) surface

Intensive effort has recently been made in search of topological insulators (TIs) that have great potential in spintronics applications. In this paper, a novel concept of overlayer induced interfacial TI phase in conventional semiconductor surface is proposed. The first-principles calculations demonstrate that a $p$-band-element $X$ $(X=\text{In}$, Bi, and Pb) decorated $d$-band surface, such as Au/Si(111) surface $[X$/Au/Si(111)] of an existing experimental system, offers a promising prototype for TIs. Specifically, Bi/Au/Si(111) and Pb/Au/Si(111) are identified to be large-gap TIs. A $p\text{\ensuremath{-}}d$ band inversion mechanism induced by growth of $X$ in the Au/Si(111) surface is revealed to function at different coverage of $X$ with different lattice symmetries, suggesting a general approach of interface orbital engineering of large-gap TIs via tuning the interfacial atomic orbital position of $X$ relative to Au.