A universal model for magnetic topological insulator multilayers

What is it about?

We discuss the magnetic and topological properties of bulk crystals and quasi-two-dimensional (quasi-2D) thin films formed by stacking intrinsic magnetized topological insulator (for example, Mn (SbxBi1−x)2X4 with X = Se,Te) septuple layers and topological insulator quintuple layers in arbitrary order. Our analysis makes use of a simplified model that retains only Dirac cone degrees of freedom on both surfaces of each septuple or quintuple layer. We demonstrate the model’s applicability and estimate its parameters by comparing with ab initio density-functional theory (DFT) calculations. We then employ the coupled Dirac cone model to provide an explanation for the dependence of thin-film properties, particularly the presence or absence of the quantum anomalous Hall effect, on film thickness, magnetic configuration, and stacking arrangement, and to comment on the design of Weyl superlattices.

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Why is it important?

Topological insulators have Dirac cone surface states protected by time-reversal symmetry (TRS). Weak magnetic order in topological insulator thin films can lead to the quantum anomalous Hall effect (QAHE), which was first realized by magnetic doping of topological insulators to establish a fragile ferromagnetic state. Recent work has established MnBi2Te4 as a structurally ordered magnetic topological insulator. We report on a theoretical study of superlattices formed from MnBi2Te4 and Bi2Te3 building blocks that employ a simplified model validated by ab initio density-functional theory. We use it to shed light on the dependence of the quantum anomalous Hall effect on film thickness, magnetic configuration, the stacking sequences of the van der Waals coupled building blocks, and bulk electronic structure.

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