# Regensburg 2019 – wissenschaftliches Programm

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# MA: Fachverband Magnetismus

## MA 4: Topological insulators and spin-dependent transport phenomena

### MA 4.4: Vortrag

### Montag, 1. April 2019, 10:15–10:30, H52

**The ***Z*_{2}** topology of bismuth** — •Irene Aguilera, Christoph Friedrich, Gustav Bihlmayer, and Stefan Blügel — Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany

The *Z*_{2} topology of bulk and thin films of pure bismuth has been
a matter of debate in the last few years.
Whereas all first-principles calculations with different levels of sophistication
predict a trivial *Z*_{2} invariant, a couple of photoemission experiments display surface states that look non-trivial.
The discrepancies between theory and experiment were originally attributed
to the failure of density functional theory (DFT)
in the prediction of band gaps, because the topological or trivial character of Bi depends only on
the “sign” of the tiny (∼15 meV) direct band gap at the L point.
In [1] we showed that quasiparticle self-consistent *GW* (QS*GW*)
calculations support the trivial character. These are, to date, the most accurate
calculations for bulk Bi in the literature. However, this did not explain
the discrepancy with experiments.
In this talk, I will explain, based on QS*GW* calculations, why the apparent contradiction between theory and
experiment is, as a matter of fact, no contradiction, and that the “topologically-looking”
experimental surface states are actually compatible with a trivial *Z*_{2} invariant. We note that we focus on the *Z*_{2} topological character only and not on the high-order topology, recently predicted for Bi.

[1] I. Aguilera *et al.*, Phys. Rev. B **91**, 125129 (2015).

Financial support from the Virtual Institute for Topological Insulators of the Helmholtz Association.