Optical properties of twisted bilayer graphene with magnetic defects

Abstract

Even when fabricated under ideal conditions twisted bilayer graphene (TBG) inevitably contains various defects which may significantly affect its physical properties. Here we comprehensively analyze the impact of typical point defects, represented by adsorbed hydrogen atoms, on the electronic and optical properties of TBG. It is shown using self-consistent tight-binding Hamiltonians that such point defects make TBG ferromagnetic, and that its ground state comprises a pair of nearly dispersionless spin-polarized energy bands around the Fermi level. Transitions to and from these bands strongly modify the infrared absorption of TBG and result in a sharp low-energy peak in its spectrum. It is also revealed that the adsorption of hydrogen atoms suppresses the circular dichroism of TBG due to the weakening of the electronic coupling between the graphene layers. Our findings will guide future experimental studies on the optical properties of TBG in realistic, impurity-rich environments.