Interaction effects on almost flat surface bands in topological insulators

Matthias Sitte, Achim Rosch, and Lars Fritz
Phys. Rev. B 88, 205107 – Published 8 November 2013

Abstract

We consider ferromagnetic instabilities of two-dimensional helical Dirac fermions hosted on the surface of three-dimensional topological insulators. We investigate ways to increase the role of interactions by means of modifying the bulk properties which in turn changes both the surface Dirac theory and the screening of interactions. We discuss both the long-ranged part of the Coulomb interactions controlled by the dimensionless coupling constant α=e2/(εvFsurf) as well as the effects of local interactions parametrized by the ratio Usurf/Dsurf of a local interaction on the surface Usurf and the surface bandwidth Dsurf. If large compared to 1, both mechanisms can induce spontaneously surface ferromagnetism, thereby gapping the surface Dirac metal and inducing an anomalous quantum Hall effect. We investigate two mechanisms which can naturally lead to small Fermi velocities vFsurf and a corresponding small bandwidth Dsurf at the surface when the bulk band gap is reduced. The same mechanisms can, however, also lead to an enhanced screening of surface interactions. While in all considered cases the long-ranged part of the Coulomb interaction is screened efficiently, α1, we discuss situations where Usurf/Dsurf becomes parametrically large compared to 1, thus inducing surface magnetism.

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  • Received 13 May 2013

DOI:https://doi.org/10.1103/PhysRevB.88.205107

©2013 American Physical Society

Authors & Affiliations

Matthias Sitte, Achim Rosch, and Lars Fritz

  • Institut für Theoretische Physik, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany

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Issue

Vol. 88, Iss. 20 — 15 November 2013

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