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HL: Fachverband Halbleiterphysik

HL 14: Topological Insulators 2 (jointly with DS, MA, HL, O) (joint session TT/HL)

HL 14.2: Vortrag

Montag, 16. März 2020, 15:15–15:30, HSZ 103

Boundary State Engineering and Topological Charge Pumps in non-Hermitian Floquet systems — •Bastian Höckendorf, Andreas Alvermann, and Holger Fehske — Institut für Physik, Universität Greifswald, Greifswald, Germany

In Hermitian topological systems, the bulk-boundary correspondence strictly constraints boundary transport to values determined by the topological properties of the bulk. We demonstrate that this constraint can be lifted in non-Hermitian Floquet insulators. Provided that the insulator supports an anomalous topological phase, non-Hermiticity allows us to modify the boundary states independently of the bulk, without sacrificing their topological nature. Non-Hermitian boundary state engineering specifically enables the enhancement of boundary transport relative to bulk motion, helical transport with a preferred direction, and chiral transport in the same direction on opposite boundaries [1]. Through dimensional reduction, the Floquet insulator reduces to a one-dimensional Floquet chain which possesses a topological phase with unidirectional transport. The topological signature of this phase are non-contractible loops in the spectrum of the Floquet propagator that are separated by an imaginary gap. We define the corresponding topological invariant as the winding number of the Floquet propagator relative to the imaginary gap and then establish that the charge transferred over one period equals the winding number. In fundamental difference to the situation for static or Hermitian chains, the chain acts as a topological charge pump [2].

[1] Phys. Rev. Lett. 123, 190403 (2019)

[2] arXiv:1911.11413