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MA: Fachverband Magnetismus
MA 7: Transport: Topological Insulators - 2D
(Joint session of DS, HL, MA, O and TT organized by TT)
MA 7.8: Vortrag
Montag, 7. März 2016, 17:00–17:15, H18
Topological Edge States with Zero Hall Conductivity in a Dimerized Hofstadter Model — •Alexander Lau1, Carmine Ortix1,2, and Jeroen van den Brink1,3 — 1Institute for Theoretical Solid State Physics, IFW Dresden, Germany — 2Institute for Theoretical Physics, Utrecht University, The Netherlands — 3Department of Physics, TU Dresden, Germany
The Hofstadter model is one of the most celebrated models for the study of topological properties of matter and allows the study of the quantum Hall effect in a lattice system. Indeed, the Hofstadter Hamiltonian harbors the topological chiral edge states that are responsible for the quantized Hall conductivity.
Here, we show that a lattice dimerization in the Hofstadtermodel opens an energy gap at half-filling. What is more, we demonstrate that even if the ensuing insulator has a Chern number equal to zero, concomitantly a doublet of edge states appear that are pinned to specific momenta. We show that the presence of these states can be understood from the topological properties of lower dimensional cuts of the system, using a mapping of the Hofstadter Hamiltonian to a collection of one-dimensional Aubry-Andre-Harper (AAH) models. A sub-set of AAH chains in this collection preserve inversion symmetry. This guarantees the presence of topologically protected doublets of end modes to which the edge states are pinned. To explicitly prove the robustness of the emerging edge states, we define and calculate the topological invariant that protects them, which turns out to be an integer invariant for inversion-symmetric AAH models.