Faraday rotations, ellipticity and circular dichroism in the magneto-optical spectrum of moir\'e superlattices

TL;DR

This paper investigates the magneto-optical properties of various van der Waals heterostructures, revealing fractal absorption spectra and differing circular dichroism effects, with notable Faraday rotation and ellipticity in transmitted light.

Contribution

It provides a comparative analysis of magneto-optical responses in multiple heterostructures, highlighting the role of symmetry breaking and fractal energy spectra.

Findings

Fractal, recursive absorption spectra observed with increasing magnetic field.

Strong circular dichroism in monolayer graphene and bilayer graphene on hBN.

Faraday rotation and ellipticity of about one degree in transmitted light.

Abstract

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 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, monolayer graphene and AB-stacked bilayer graphene on hexagonal boron nitride show specifically strong circular dichroism, 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.