Cutting off the non-Hermitian boundary from an anomalous Floquet topological insulator

In two-dimensional anomalous Floquet insulators, chiral boundary states can spectrally detach from the bulk bands through non-Hermitian boundary state engineering. We show that this spectral detachment enables spatial detachment: The non-Hermitian boundary can be physically cut off from the bulk while retaining its topological transport properties. The resulting one-dimensional chain is identified as a non-Hermitian Floquet chain with non-zero winding number. Through the spatial detachment, the conventional bulk-boundary correspondence is recovered in the anomalous Floquet insulator. We demonstrate our theoretical findings for the standard model of an anomalous Floquet insulator and discuss their experimental relevance.