# Berlin 2018 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 20: Focussed Session: Geometry- and Topology-Controlled Nanoarchitectures II

### HL 20.5: Vortrag

### Dienstag, 13. März 2018, 15:15–15:30, EW 015

**Intrinsic spin-orbit coupling and spin-Hall effect in graphene** — •Marta Prada^{1}, Jonas Sichau^{2}, and Robert H Blick^{2} — ^{1}I. Institute for Theoretical Physics, Jungiusstr. 9, Hamburg (Germany) — ^{2}Center for Hybrid Nanostructures (ChyN), Luruper Chaussee 149, Hamburg (Germany)

The fundamental assumption of graphene is the celebrated linear energy dispersion relation for charge carriers, as it occurs in the Dirac equation. However, zooming in the low energy scales, a finite gap, and hence, a finite mass is expected. The magnitude of this gap in graphene is of great interest, determining the possibility to observe a topological (spin Hall) insulator. However, controversy exists around the value of this gap, with theoretical predictions varying within two orders of magnitude, while an experimental value has not been determined to this date.

Here, we present evidence that intrinsic spin-orbit interaction in monolayer graphene leads to a measurable bulk gap of 42 μeV [J. Sichau, M. Prada, T. J. Lyon, B. Bosnjak, L. Tiemann, and R. H. Blick arXiv:1709.05705 (2017).]. We experimentally resolve the spin and pseudo-spin states using microwave excitation in a resistively detected electron spin resonance experiment. We develop a theoretical model that includes the effects of the d-orbitals in a rectangular sample of graphene, and find perfect agreement with the experimental data. Our results are consistent with a spin Hall insulator to a Dirac semimetal phase transition.