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

The introduction of magnetic order into topological band structure gives to new phenomena such as proximity effect and nonreciprocal magnetoelectric effects. We couple the helical edges states in a 2D topological insulator, monolayer WTe₂, to a 2D layered antiferromagnet, CrI₃. 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 state. 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.