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Graphene as two-dimensional conductor and topologial insulators which possess two-dimensional metallic surface states around an insulating volume share also quasirelativistic properties of their charge carriers. Their characteristic linear E(k) band dispersions can be observed as so-called Dirac cones in angle-resolved photoelectron spectroscopy. In graphene, they are caused by pseudospin properties, in topological insulators such as Bi2Se3 by the electron spin. This opens the possibility to manipulate transport properties by opening a surface band gap at the Dirac crossing point through breaking of the sublattice symmetry of graphene or the time-reversal symmetry of topological insulators. In the talk, examples are shown where these attempts lead to surprising results. In a further step, graphene is made spin dependent by an extrinsic spin orbit interaction. The resulting spin polarization is in the surface plane - the same is the case with topological insulators. The opening of the Dirac point by symmetry breaking should in both cases turn the spin perpendicular to the surface. This is demonstrated for graphene. For topological insulators, we show that the spin can be turned out of the plane by polarized light in the photoemission process.

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Oliver Rader, Helmholtz-Zentrum Berlin
Seminar Room of the Institute of Physics II
Contact: Thomas Michely