Nonlinear optical response of Type-II Weyl fermions in two dimensions

We present a theoretical model to study the nonlinear optical response of materials with a low-energy spectrum characterised by strongly tilted, type-II, Weyl cones in two dimensions, which we call 2D Weyl materials. Our findings reveal that the tilted nature of the Weyl cones is responsible for the appearance of even harmonics in the nonlinear signal, as well as its strong polarisation dependence. We discuss how it is possible to control such nonlinear response and envision how 2D Weyl materials can be used to realise novel photonic devices for sensing applications.