Discovery of magnetic topological insulators using chemistry

In designing magnetic topological insulating states one often runs into mutually exclusive co-existence of topology and electron correlations. In order to achieve an intrinsic magnetic topological insulator state, there needs to be a separation between the density of states close to the Fermi level and the states from magnetism. Using this requirement, we identify Zintl compounds to be promising to find a sweet spot between topology and electron correlations. Zintl compounds have rocksalt-like charge separation between the cationic and anionic frameworks that are charge separated from one another. If the cationic framework is magnetic and the anionic framework is non-magnetic, consists of heavy atoms, and has covalent bonding, then these serve as essential structural motifs for magnetic topological insulators. Using this concept, we identify the Eu5M2X6 (M = Ga,In,Tl, X = Sb,Bi) family of materials as a rich source of topologically trivial and non-trivial insulators. In this work we will present the synthesis, magnetism, optical and transport behavior of members of this family with an aim of identifying an intrinsic axion insulator.