Superlattices of Gadolinium and Bismuth Based Thallium Dichalcogenides as Potential Magnetic Topological Insulators

Using relativistic spin-polarized density functional theory calculations we investigate magnetism, electronic structure and topology of the ternary thallium gadolinium dichalcogenides TlGd [Formula: see text] ([Formula: see text] Se and Te) as well as superlattices on their basis. We find TlGd [Formula: see text] to have an antiferromagnetic exchange coupling both within and between the Gd layers, which leads to frustration and a complex magnetic structure. The electronic structure calculations reveal both TlGdSe [Formula: see text] and TlGdTe [Formula: see text] to be topologically trivial semiconductors. However, as we show further, a three-dimensional (3D) magnetic topological insulator (TI) state can potentially be achieved by constructing superlattices of the TlGd [Formula: see text] /(TlBi [Formula: see text]) [Formula: see text] type, in which structural units of TlGd [Formula: see text] are alternated with those of the isomorphic TlBi [Formula: see text] compounds, known to be non-magnetic 3D TIs. Our results suggest a new approach for achieving 3D magnetic TI phases in such superlattices which is applicable to a large family of thallium rare-earth dichalcogenides and is expected to yield a fertile and tunable playground for exotic topological physics.