Epitaxial growth of 2D van der Waals magnets and heterostructures with topological insulators

I will discuss our latest advances on the epitaxial growth of 2D van der Waals (vdW) magnets and their integration with topological insulators (TI). This work is motivated by the realization of topological phases such as the quantum anomalous Hall effect and highly efficient spin-orbit torque produced by TIs.

Our initial studies of MnSe₂ growth on Bi₂Se₃ showed a tendency for the interdiffusion of Mn into the Bi₂Se₃. [1]. This ultimately led to the synthesis of MnBi₂Se₄ (MBS), a new magnetic TI [2]. Interestingly, the vdW phase is not the thermodynamically stable phase and bulk crystals do not exist, so the epitaxial stabilization of MBS creates the opportunity to explore the magnetic and topological properties of this material. We find that MBS is a layered antiferromagnet, similar to MnBi₂Te₄, but a difference is that the magnetic moments lie in the plane of the film. Angle-resolved photoemission experiments show the presence of a topological surface state with Dirac dispersion.

For bilayers of 2D magnets and TIs, we have developed FGT films on Bi₂Te₃. We first optimized FGT by studying its growth on Ge(111) substrates, where we find that kinetic considerations play a major role [3]. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111). Subsequently, we have developed the growth of FGT on Bi₂Te₃ for the integration of 2D magnets with TIs. Interestingly, we observe room temperature ferromagnetism in FGT/Bi₂Te₃ heterostructures by varying the growth conditions.