New Universal Type of Interface in the Magnetic Insulator/Topological Insulator Heterostructures

Abstract

Magnetic proximity effect at the interface between magnetic and topological insulators (MIs and TIs) is considered to have great potential in spintronics as, in principle, it allows realizing the quantum anomalous Hall and topological magneto-electric effects (QAHE and TME). Although an out-of-plane magnetization induced in a TI by the proximity effect was successfully probed in experiments, first-principles calculations reveal that a strong electrostatic potential mismatch at abrupt MI/TI interfaces creates harmful trivial states rendering both the QAHE and TME unfeasible in practice. Here on the basis of recent progress in formation of planar self-assembled single layer MI/TI heterostructure (T. Hirahara et al. Nano Lett.20171734933500), we propose a conceptually new type of the MI/TI interfaces by means of density functional theory calculations. By considering MnSe/Bi2Se3, MnTe/Bi2Te3, and EuS/Bi2Se3 we demonstrate that, instead of a sharp MI/TI interface clearly separating the two subsystems, it is energetically far more favorable to form a built-in interface via insertion of the MI film inside the TI’s surface quintuple layer (e.g., Se–Bi–Se–[MnSe]–Bi–Se) where it forms a bulk-like MI structure. This results in a smooth MI-to-TI connection that yields the interface electronic structure essentially free of trivial states. Our findings open a new direction in studies of the MI/TI interfaces and restore their potential for the QAHE and TME observation.

Do topology and ferromagnetism cooperate at the EuS/Bi2Se3 interface?

“…Some calculations further predict an EuS derived band which dips below E F at the Mpoint [31]. However, recent DFT results suggest that the presence of these trivial states depends on the assumed interface structure [55]. Indeed, we observe none of these bands experimentally.…”

Interplay of Topological States on TI/TCI Interfaces

“…The strategy of the smooth interface construction is based on a recently proposed novel type of interface between a magnetic insulator and a topological insulator of the Bi Se family [ 22 , 33 , 34 ]. It implies the immersion of the epitaxially deposited magnetic atoms into the surface quintuple layer of a Bi Se substrate which results in formation of the magnetic film sandwiched by the remnant layers of this quintuple layer.…”

“…An example of spontaneous formation of the smooth interface is formation of well-ordered hexagonal MnBi Se SL [ 32 ] on top of Bi Se TI due to immersion of the epitaxially deposited Mn and Se atoms into the surface quintuple layer of a TI [ 22 ]. Following this procedure, it is possible to grow relatively thick films sandwiched by the remnant layers of the TI structural block [ 33 ] that has been realized very recently [ 34 ]. In this context, the ideal ingredient for TI/SnTe smooth interface can be SnBi Te , which is naturally composed of SL blocks which include SnTe bilayer in the middle.…”

Topological properties of SnSe/EuS and SnTe/CaTe interfaces

“…Both surface slab models (with a vacuum region) and periodic heterostructures are considered. We note that diffusion at the interface [36,37] is not considered here. We find that a gapped surface state appears at the SnSe(111)/EuS(111) interface.…”