ETD

• condensed matter
• moire materials
• optical phenomena
• strong correlations

Moiré materials, composed of two atomically-thin crystals twisted relative to each other, are intrinsically chiral. The emergence of a pair of flat bands in twisted bilayer graphene at magic angles has been analytically predicted through low-energy effective continuum models. In the presence of flat bands, the kinetic energy becomes negligible, and interactions between electrons dominate the underlying physics. The physical consequences of the intrinsic chirality of these platforms have often been neglected, as it does not affect the bandstructure or the eigenstates. In this Thesis, we discuss how the intrinsic chirality of twisted bilayer graphene affects particular optical phenomena—e.g. natural optical activity—that are able to discern between the two enantiomers. We derive explicit expressions for optical observables in the context of Kubo linear response theory, and explore how the interlayer coupling plays a fundamental role. We study the behavior of the angle of rotation of polarized light as a function of the twist angle near and at the magic angle. We observe how the flattening of the lowest bands enhances the magnitude of the optical rotation at zero filling, and we predict a frequency-independent, temperature-dependent constant background stemming from the contribution of just the two flat bands. We perform numerical simulations of this quantity by using the two main effective continuum model Hamiltonians. Our numerical calculations are mainly carried out in the non-interacting limit, but we also present results including electron-electron interactions implemented via a self-consistent Hartree theory. We explicitly observe the constant background and its distinctive temperature dependence.