Plasmons in Two-Dimensional Topological Insulators

We analyze collective excitations in models of two-dimensional topological insulators, determining their bulk and surface properties using the random phase approximation in real and reciprocal space, respectively. In the two-dimensional extension of the Su-Schrieffer-Heeger model, we reveal characteristic signatures that distinguish distinct phases by their plasmonic response. Bulk features are controlled by the overlap of the single particle wave functions, which in turn lead to a hardening and softening of inter- and intra-band plasmonic branches, respectively. In real space, plasmonic modes governed by electronic transitions involving the mid-gap topological edge states are found, resulting in characteristic induced charge-density distributions strongly localized at the boundaries of the system. In the Haldane model, single-particle band structure details are instead identified as the dominant contribution influencing bulk plasmonic responses in different topological phases.