Molecular beam epitaxy growth and structure of self-assembled Bi₂Se₃/Bi₂MnSe₄ multilayer heterostructures

We demonstrate that the introduction of an elemental beam of Mn during the molecular beam epitaxial growth of Bi₂Se₃ results in the formation of layers of Bi₂MnSe₄ that intersperse between layers of pure Bi₂Se₃. This study revises the assumption held by many who study magnetic topological insulators (TIs) that Mn incorporates randomly at Bi-substitutional sites during epitaxial growth of Mn:Bi₂Se₃. Here, we report the formation of thin film magnetic TI Bi₂MnSe₄ with stoichiometric composition that grows in a self-assembled multilayer heterostructure with layers of Bi₂Se₃, where the number of Bi₂Se₃ layers separating the single Bi₂MnSe₄ layers is approximately defined by the relative arrival rate of Mn ions to Bi and Se ions during growth, and we present its compositional, structural, and electronic properties. We support a model for the epitaxial growth of Bi₂MnSe₄ in a near-periodic self-assembled layered heterostructure with Bi₂Se₃ with corresponding theoretical calculations of the energetics of this material and those of similar compositions. Computationally derived electronic structure of these heterostructures demonstrates the existence of topologically nontrivial surface states at sufficient thickness.