Magnetic proximity and nonreciprocal current switching in a monolayer WTe 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. The ability to simply stack very different two-dimensional van der Waals materials in intimate contact permits a different approach. Here we use this approach to couple the helical edges states in a two-dimensional topological insulator, monolayer WTe (refs. ), to a two-dimensional layered antiferromagnet, CrI (ref. ). We find that the edge conductance is sensitive to the magnetization state of the CrI, and the coupling can be understood in terms of an exchange field from the nearest and next-nearest CrI layers that produces a gap in the helical edge. We also find that the nonlinear edge conductance depends on the magnetization of the nearest CrI 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 CrI.