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Edge bands and vertical transport in topological insulator/magnetic insulator heterostructures

The low-energy band-structure of electrons propagating on a lateral surface of a heterostructure consisting of three dimensional topological insulator (TI) and magnetic insulator layers has been calculated. The energy spectrum is highly tunable depending on the relation between the interlayer tunneling amplitude, Zeeman energy and surface potential. A ratio between the first two parameters controls a topological transition between chiral and helical surface state band-structures. In the former case localized states, whose wave-functions are confined near single TI layers, emerge in a narrow parameter range where they coexist with itinerant states. In regular superlattices these localized states form a flat band in the vertical direction. Such a localization has a topological origin. It is associated with a specific spatial spin texture of these states. The localized states vanish upon the topological phase transition from the anomalous quantum Hall regime to a trivial phase characterized by an anisotropic Dirac cone on the lateral surface of the heterostructure.