SKM 2023 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 36: Topological Insulators

TT 36.5: Talk

Wednesday, March 29, 2023, 16:00–16:15, HSZ 103

Mixed higher-order topology: boundary non-Hermitian skin effect induced by a Floquet bulk — •Hui Liu and Ion Cosma Fulga — Leibniz Institute for Solid State and Materials Research, Dresden

We show that anomalous Floquet topological insulators generate intrinsic, non-Hermitian topology on their boundary. As a consequence, removing a boundary hopping from the time-evolution operator stops the propagation of chiral edge modes, leading to a non-Hermitian skin effect. This does not occur in Floquet Chern insulators, however, in which boundary modes continue propagating. By evaluating the local density of states, we found that the resulting non-Hermitian skin effect is critical, i.e. scale-invariant, due to the nonzero coupling between the bulk and the edge. Further, it is a consequence of the nontrivial topology of the bulk Floquet operator, which we show by designing a real-space topological invariant. Our work introduces a form of ’mixed’ higher-order topology, where a bulk system characterized by Floquet topology produces a boundary system characterized by non-Hermitian topology, without the need for any added perturbations. This opens an alternate direction in the study of topological classifications, and provides a route towards generating non-Hermitian skin effects by means of periodic driving.