title: Plasmons due to the interplay of Dirac and Schrödinger fermions.
abstract: We study the interplay between Dirac and Schrödinger fermions in the polarization properties of a two-dimensional electron gas (2DEG). Specifically, we analyze the low-energy sector of narrow-gap semiconductors described by a two-band Kane model. In the context of quantum spin Hall insulators, particularly, in Hg(Cd)Te quantum wells, this model is named the Bernevig-Hughes-Zhang model. Interestingly, it describes electrons with intermediate properties between Dirac and Schrödinger fermions. We calculate the dynamical dielectric function of such a model at zero temperature within random phase approximation. Surprisingly, plasmon resonances are found in the intrinsic (undoped) limit, whereas they are absent-in that limit-in graphene as well as ordinary 2DEGs. Additionally, we demonstrate that the optical conductivity offers a quantitative way to identify the topological phase of Hg(Cd)Te quantum wells from a bulk measurement.
authors.affiliation: Institute of Theoretical Physics and Astrophysics, University of Würzburg, D-97074 Würzburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Juergens
authors.affiliation: Institute of Theoretical Physics and Astrophysics, University of Würzburg, D-97074 Würzburg, Germany.
authors.forename: Paolo
authors.initials: P
authors.lastname: Michetti
authors.affiliation: Institute of Theoretical Physics and Astrophysics, University of Würzburg, D-97074 Würzburg, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Trauzettel