A robust weak topological insulator in a bismuth halide Bi4Br2I2

TL;DR

This paper identifies Bi4Br2I2 as a highly promising weak topological insulator with a large band gap, using a combination of theoretical calculations and experimental techniques, opening new avenues for research and applications.

Contribution

It introduces a novel design approach for weak topological insulators and demonstrates Bi4Br2I2 as the most robust candidate with the largest band gap among known WTIs.

Findings

Bi4Br2I2 is an ideal weak topological insulator.

It has the largest band gap (~230 meV) among WTI candidates.

Experimental and theoretical methods confirm its topological properties.

Abstract

We apply a topological material design concept for selecting a bulk topology of 3D crystals by different van-der-Waals stacking of 2D topological insulator layers, and find a bismuth halide Bi4Br2I2 to be an ideal weak topological insulator (WTI) with the largest band gap (~230 meV) among all the WTI candidates, by means of angle-resolved photoemission spectroscopy (ARPES), density functional theory (DFT) calculations, and resistivity measurements. Our results vastly expand future opportunities for fundamental research and device applications with a robust WTI.