Regensburg 2013 – scientific programme

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MA: Fachverband Magnetismus

MA 46: Topological Insulators 5 (jointly with DS, HL, MA, and O)

MA 46.12: Talk

Friday, March 15, 2013, 12:30–12:45, H18

Interaction effects on almost flat surface bands in topological insulators — •Matthias Sitte, Lars Fritz, and Achim Rosch — Universität zu Köln, Institut für Theoretische Physik, Zülpicher Str. 77, 50937 Köln, Deutschland

We investigate ferromagnetic instabilities of the two-dimensional helical Dirac fermions hosted on the surface of three-dimensional topological insulators. We concentrate on ways to increase the role of interactions by means of modifying the bulk properties which in turn changes the surface Dirac theory characteristics. We discuss both long-ranged Coulomb interactions controlled by the dimensionless coupling constant α = e²/(ℏ є v_F^surf) as well as short-ranged Hubbard-like interactions of strength U which can induce spontaneous surface ferromagnetism, thereby gapping the surface Dirac metal. In both cases, we find that a prerequisite for observing this effect is to reduce the Fermi velocity v_F^surf, and we consider different mechanisms to achieve this. While for long-ranged Coulomb interactions we find that screening hinders ferromagnetism, for short-ranged interactions screening is not that vital and the instability can prevail.