Epitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface

TL;DR

This paper demonstrates, through first-principles calculations, the epitaxial growth of a large-gap quantum spin Hall insulator on a semiconductor surface, revealing a substrate orbital filtering effect that induces topological phases.

Contribution

It introduces a novel method for growing large-gap topological insulators on semiconductor surfaces using substrate orbital filtering effects, enabling new topological phases.

Findings

Bi overlayers form stable hexagonal lattices on Si(111) surfaces.

The Bi overlayer exhibits a 0.8 eV energy gap with a QSH state.

Substrate orbital filtering induces topological phases in the overlayer.

Abstract

Formation of topological quantum phase on conventional semiconductor surface is of both scientific and technological interest. Here, we demonstrate epitaxial growth of 2D topological insulator, i.e. quantum spin Hall (QSH) state, on Si(111) surface with a large energy gap, based on first-principles calculations. We show that Si(111) surface functionalized with 1/3 monolayer of halogen atoms [Si(111)-sqrt(3) x sqrt(3)-X (X=Cl, Br, I)] exhibiting a trigonal superstructure, provides an ideal template for epitaxial growth of heavy metals, such as Bi, which self-assemble into a hexagonal lattice with high kinetic and thermodynamic stability. Most remarkably, the Bi overlayer is "atomically" bonded to but "electronically" decoupled from the underlying Si substrate, exhibiting isolated QSH state with an energy gap as large as 0.8 eV. This surprising phenomenon is originated from an intriguing substrate orbital filtering effect, which critically select the orbital composition around the Fermi level leading to different topological phases. Particularly, the substrate-orbital-filtering effect converts the otherwise topologically trivial freestanding Bi lattice into a nontrivial phase; while the reverse is true for Au lattice. The underlying physical mechanism is generally applicable, opening a new and exciting avenue for exploration of large-gap topological surface/interface states.