Excitonic effects on dichroic phenomena in van der Waals layered materials

The layered structure of two-dimensional van der Waals materials provides an ideal platform to explore optical responses relying on the spatially dispersive electromagnetic fields. Meanwhile, owing to suppressed dielectric screening, the influence of Coulomb interaction on these optical responses cannot be neglected. Here, we use the generating functional formalism to derive the spatially dispersive optical conductivity incorporating the excitonic effect. It can be directly connected to circular dichroism and nonreciprocal directional dichroism of the material. We use twisted MoTe2 moiré structure to demonstrate that excitons can strongly enhance these dichroic responses. Our results offer a promising route to use excitonic and correlation effects to tune and characterize the chirality and nonreciprocity of materials.