A first-principles study of bilayer 1T'-WTe2/CrI3: A candidate topological spin filter

The ability to manipulate electronic spin channels in 2D materials is crucial for realizing next-generation spintronics. Spin filters are spintronic components that polarize spins using external electromagnetic fields or intrinsic material properties like magnetism. Recently, topological protection from backscattering has emerged as an enticing feature through which the robustness of 2D spin filters might be enhanced. In this work, we propose and then characterize one of the first 2D topological spin filters: bilayer CrI3/1T'-WTe2. To do so, we use a combination of Density Functional Theory and maximally localized Wannier functions to demonstrate that the bilayer (BL) satisfies the principal criteria for being a topological spin filter; namely that it is gapless, exhibits charge transfer from WTe2 to CrI3 that renders the BL metallic despite the CrI3 retaining its monolayer ferromagnetism, and does not retain the topological character of monolayer 1T'-WTe2. In particular, we observe that the atomic magnetic moments on Cr from DFT are approximately 3.2 mB/Cr in the BL compared to 2.9 mB/Cr with small negative ferromagnetic (FM) moments induced on the W atoms in freestanding monolayer CrI3. Subtracting the charge and spin densities of the constituent monolayers from those of the BL further reveals spin-polarized charge transfer from WTe2 to CrI3. We find that the BL is topologically trivial by showing that its Chern number is zero. Altogether, this evidence indicates that BL 1T'-WTe2/CrI3 is gapless, magnetic, and topologically trivial, meaning that a terraced WTe2/CrI3 BL heterostructure in which only a portion of a WTe2 monolayer is topped with CrI3 is a promising candidate for a 2D topological spin filter. Our results further suggest that 1D chiral edge states may be realized by stacking strongly hybridized FM monolayers, like CrI3, atop 2D nonmagnetic Weyl semimetals like 1T'-WTe2.