Band Structure Engineering of Multinary Chalcogenide Topological Insulators

TL;DR

This paper explores how chemical ordering in multinary chalcogenide compounds can be used to engineer larger topological insulator band gaps, advancing the design of materials with significant non-trivial electronic properties.

Contribution

It identifies key parameters influencing topological band gaps and demonstrates that specific quaternary compounds can achieve larger gaps through chemical tuning.

Findings

Ag2HgPbSe4 has the largest TI band gap of 47 meV.

Large negative crystal field splitting and s-p band gap are crucial for big non-trivial gaps.

Chemical ordering in multinary compounds enhances topological insulator properties.

Abstract

Topological insulators (TIs) have been found in strained binary HgTe and ternary I-III-VI2 chalcopyrite compounds such as CuTlSe2 which have inverted band structures. However, the non-trivial band gaps of these existing binary and ternary TIs are limited to small values, usually around 10 meV or less. In this work, we reveal that a large non-trivial band gap requires the material having a large negative crystal field splitting $\Delta_{CF}$ at top of the valence band and a moderately large negative $s-p$ band gap $E_g^{s-p}$. These parameters can be better tuned through chemical ordering in multinary compounds. Based on this understanding, we show that a series of quaternary I2-II-IV-VI4 compounds, including Cu2HgPbSe4, Cu2CdPbSe4, Ag2HgPbSe4 and Ag2CdPbTe4 are TIs, in which Ag2HgPbSe4 has the largest TI band gap of 47 meV because it combines the optimal values of $\Delta_{CF}$ and $E_g^{s-p}$.