Prediction of weak topological insulators in layered semiconductors

TL;DR

This paper predicts weak topological insulators in layered honeycomb semiconductors using ab initio calculations, highlighting the importance of odd-layer structures and potential for large-gap surface states.

Contribution

It introduces a new class of weak topological insulators in layered semiconductors and identifies specific structures like KHgSb as promising candidates.

Findings

KHgSb has a large bulk energy gap of 0.24 eV.

Side surfaces host metallic Dirac cone states.

Odd-layered structures are key for weak topological insulators.

Abstract

We report the discovery of weak topological insulators by ab initio calculations in a honeycomb lattice. We propose a structure with an odd number of layers in the primitive unit-cell as a prerequisite for forming weak topological insulators. Here, the single-layered KHgSb is the most suitable candidate for its large bulk energy gap of 0.24 eV. Its side surface hosts metallic surface states, forming two anisotropic Dirac cones. Though the stacking of even-layered structures leads to trivial insulators, the structures can host a quantum spin Hall layer with a large bulk gap, if an additional single layer exists as a stacking fault in the crystal. The reported honeycomb compounds can serve as prototypes to aid in the finding of new weak topological insulators in layered small-gap semiconductors.