Plasmonic Quantum Dots in Twisted Bilayer Graphene

Abstract

We derive a material-realistic real-space many-body Hamiltonian for twisted bilayer graphene from first principles, including both single-particle hopping terms for pz electrons and long-range Coulomb interactions. By disentangling low-and high-energy subspaces of the electronic dispersion, we are able to utilize state-of-the-art constrained Random Phase Approximation calculations to reliably describe the non-local background screening from the high-energy s, px, and py electron states for arbitrary twist angles. The twist-dependent low-energy screening from pz states is subsequently added to obtain a full screening model. We use this approach to study real-space plasmonic patterns in electron-doped twisted bilayer graphene supercells and find, next to classical dipole-like modes, also twist-angle-dependent plasmonic quantum-dot-like excitations with s and p symmetries. Based on their inter-layer charge modulations and their footprints in the electron energy loss spectrum, we can classify these modes into "bright" and "dark" states, which show different dependencies on the twist angle.