Control of Plasmons in Topological Systems

Topological insulators are characterized by non-trivial symmetry-protected topological order which leads to fundamentally novel band structure and electronic states. Topological features also manifest themselves in the collective excitations. For example, localized as well as propagating plasmon modes are observed on the surface of topologically non-trivial systems. In this work, we study plasmonic excitations in a topological system with a partially filled band, focusing on the effects of Coulomb interactions upon manipulating internal degrees of freedom, such as the sub-lattice orbitals. While the symmetry properties of the topological system characterize the electronic wavefunctions over these orbitals, the Coulomb interactions in the system also depend on the real-space configuration of these orbitals. Together, these factors determine the dielectric response function and the dynamical screening in the system. We find that through control of these internal orbitals we can tune the intra- and inter-band screening effect, and ultimately suppress or enhance plasmon dispersions in different energy regimes. We propose simple ideas on how to observe these effects in experiments.