Regensburg 2016 – scientific programme

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SYES: Symposium Frontiers of Electronic Structure Theory: Focus on Topology and Transport

SYES 5: Frontiers of Electronic Structure Theory: Focus on Topology and Transport III

SYES 5.6: Talk

Wednesday, March 9, 2016, 16:45–17:00, H24

Two-dimensional topological phases and electronic spectra of topological insulator thin films from GW calculations — •Tobias Förster, Peter Krüger, and Michael Rohlfing — Institut für Festkörpertheorie, Westfälische Wilhelms-Universität, 48149 Münster, Germany

We have investigated topological and electronic properties of thin films of the topological insulators Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃ with thicknesses from one to six quintuple layers employing the GW method. The quasiparticle band structures show highly improved agreement with experiments compared to DFT. In addition to a correction of the band gaps, the energetic positions and dispersions of the surface states change significantly around Γ [1]. The common approach of taking the diagonal elements of the self-energy Σ as quasiparticle energies and leaving the wave functions unchanged yields unphysical results which can be overcome by diagonalizing H^QP. The origin of the respective off-diagonal elements in (Σ − V_xc) will be discussed. As the wave functions are updated, the two-dimensional topological phases (quantum spin Hall or trivial) in GW differ from DFT for many systems. On the basis of our results, we further argue that one cannot unambiguously conclude the topological phase from fits to ARPES band structures as performed in recent experimental studies.

[1] T. Förster, P. Krüger, and M. Rohlfing, Phys. Rev. B 92, 201404(R) (2015)