Magnetic proximity and nonreciprocal current switching in a monolayer WTe₂ helical edge

The integration of diverse electronic phenomena, such as magnetism and nontrivial topology, into a single system is normally studied either by seeking materials that contain both ingredients, or by layered growth of contrasting materials^1-9. The ability to simply stack very different two-dimensional van der Waals materials in intimate contact permits a different approach^10,11. Here we use this approach to couple the helical edges states in a two-dimensional topological insulator, monolayer WTe₂ (refs. ^12-16), to a two-dimensional layered antiferromagnet, CrI₃ (ref. ¹⁷). We find that the edge conductance is sensitive to the magnetization state of the CrI₃, and the coupling can be understood in terms of an exchange field from the nearest and next-nearest CrI₃ layers that produces a gap in the helical edge. We also find that the nonlinear edge conductance depends on the magnetization of the nearest CrI₃ layer relative to the current direction. At low temperatures this produces an extraordinarily large nonreciprocal current that is switched by changing the antiferromagnetic state of the CrI₃.