Faraday rotations, ellipticity, and circular dichroism in magneto-optical spectrum of moire superlattices*

We study the magneto-optical conductivity of a number of van der Waals heterostructures, namely, twisted bilayer graphene, AB-AB and AB-BA stacked twisted double bilayer graphene and monolayer graphene and AB-stacked bilayer graphene on hexagonal boron nitride. As the magnetic field increases, the absorption spectrum exhibits a self-similar recursive pattern reflecting the fractal nature of the energy spectrum. Whilst twisted bilayer graphene displays only weak circular dichroism, the other four structures display strong circular dichroism with monolayer graphene and AB-stacked bilayer graphene on hexagonal boron nitride being particularly pronounced owing to strong inversion symmetry breaking properties of the hexagonal boron nitride layer. As the left and right circularly polarized light interact with these structures differently, plane-polarized incident light undergoes a Faraday rotation and gains an ellipticity when transmitted. The size of the respective angles is on the order of a degree.

Automated summary

The study investigates the magneto-optical conductivity of various van der Waals heterostructures, revealing a self-similar recursive absorption spectrum pattern with increasing magnetic field. Different structures exhibit varying degrees of circular dichroism, with Faraday rotation and ellipticity observed in plane-polarized incident light interacting with the structures.