Monolayer MnBi 2 Te 4 : Atomic-scale insights into the 2D limit of an antiferromagnetic topological insulator

As the first intrinsic antiferromagnetic topological insulator, MnBi₂Te₄ offers a platform for investigating topological phenomena driven by magnetism. Prior studies focused on bulk single crystals and exfoliated flakes, but the extreme two-dimensional (2D) limit remains underexplored, despite theoretical predictions of exotic behavior. In particular, synthesis and atomic-scale characterization of ultrathin MnBi₂Te₄ films remain challenging. Here we explore molecular beam epitaxy grown MnBi₂Te₄ thin films down to a single-layer thickness. Structural characterization via electron and x-ray diffraction, atomic force microscopy, and scanning tunneling microscopy confirms layer-by-layer growth and high crystallinity, while magnetotransport measurements show the expected magnetic signatures. Interestingly, scanning tunneling microscopy and quasiparticle interference imaging reveal Dirac-like surface states that persist even in monolayer films and monolayer islands. Our experiments provide elusive atomic-scale insights into the band structure of MnBi₂Te₄ in the 2D limit and under lateral confinement, and establish a foundation for the synthesis of heterostructures based on monolayer MnBi₂Te₄ and device applications.