Band structure engineering of multinary chalcogenide topological insulators

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 nontrivial 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 nontrivial band gap requires the material to have a large negative crystal field splitting Delta(CF) at the 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 I-2-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).