# Berlin 2018 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 7: Topological insulators I (joint session HL/TT)

### HL 7.6: Vortrag

### Montag, 12. März 2018, 10:45–11:00, A 151

**Mixed topological semimetals in two-dimensional spin-orbit ferromagnets** — •Chengwang Niu^{1}, Jan-Philipp Hanke^{1}, Patrick M. Buhl^{1}, Hongbin Zhang^{2}, Gustav Bihlmayer^{1}, Daniel Wortmann^{1}, Stefan Blügel^{1}, and Yuriy Mokrousov^{1} — ^{1}Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany — ^{2}Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany

Topological states of matter and ferromagnetism in two dimensions are nowadays two of the most intriguing and intensively researched fields in solid state physics. Here, we predict that diverse topological semimetallic phases can be obtained in 2D ferromagnets as a consequence of the spin-orbit driven changes in the electronic structure as the magnetization direction is varied. We show that the most natural way to classify these phases lies in analyzing either points or lines of degeneracies which occur in an extended phase space of Bloch vector and the magnetization direction. The emergence of the corresponding topological states, which we refer to as mixed Weyl semimetal and mixed nodal line semimetal, respectively, can be thereby confirmed by accessing corresponding topological invariants and edge states. We demonstrate the possible complexity of the topological phase diagram of 2D ferromagnets based on several model systems, and, using density functional theory, we identify two realistic examples exhibiting mixed Weyl semimetal and mixed nodal line semimetal phases.

This work was supported by SPP 1666 of the DFG.