Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 28: Transport: Topological insulators 2 (TT with HL/DS)

HL 28.8: Talk

Tuesday, March 17, 2015, 11:45–12:00, H 3005

Interplay of topology and interactions in the quantum Hall regime of two-dimensional topological insulators — •Stefan Jürgens, Maxim Kharitonov, and Björn Trauzettel — Institute of Theoretical Physics and Astrophysics, University of Würzburg, D-97074 Würzburg, Germany

We study a class of two-dimensional topological insulators, in which the single-particle edge states are preserved in the presence of the magnetic field by a symmetry (e.g., crystalline) other than time-reversal. We focus on the vicinity of the crossing point between the zero-mode Landau levels. At half-filling, Coulomb interactions become particularly strong and lead to the formation of the quantum Hall "ferromagnetic" state with gapped charge excitations in the bulk. We identify the phases of this state that have gapped or gapless collective charge edge excitations and are characterized by the presence or absence of spontaneous symmetry breaking. The transitions between these phases can occur either continuously (via second order) or abruptly (via first order), depending on the parameters of the system. These transitions are accompanied by the corresponding behavior of the egde gap, which could be detected in transport measurements. Our findings provide an example of the interplay of topological and interaction-induced (spontaneous symmetry breaking) phenomena in the strong coupling regime.