Dual topological characterization of non-Hermitian Floquet phases

TL;DR

This paper introduces a dual topological characterization scheme for non-Hermitian Floquet systems, enabling the analysis of their topological phases in both momentum and real space without constructing the generalized Brillouin zone.

Contribution

It presents a novel dual scheme for characterizing non-Hermitian Floquet topological phases in momentum and real space, simplifying analysis and predicting edge modes.

Findings

Topological phases characterized by winding numbers that jump between integers and half-integers.

Open boundary conditions reveal a Floquet open boundary winding number predicting edge modes.

Avoids the complex task of constructing the generalized Brillouin zone for non-Hermitian Floquet systems.

Abstract

Non-Hermiticity is expected to add far more physical features to the already rich Floquet topological phases of matter. Nevertheless, a systematic approach to characterize non-Hermitian Floquet topological matter is still lacking. In this work we introduce a dual scheme to characterize the topology of non-Hermitian Floquet systems in momentum space and in real space, using a piecewise quenched nonreciprocal Su-Schrieffer-Heeger model for our case studies. Under the periodic boundary condition, topological phases are characterized by a pair of experimentally accessible winding numbers that make jumps between integers and half-integers. Under the open boundary condition, a Floquet version of the so-called open boundary winding number is found to be integers and can predict the number of pairs of zero and $\pi$ Floquet edge modes coexisting with the non-Hermitian skin effect. Our results indicate that a dual characterization of non-Hermitian Floquet topological matter is necessary and also feasible because the formidable task of constructing the celebrated generalized Brillouin zone for non-Hermitian Floquet systems with multiple hopping length scales can be avoided. This work hence paves a way for further studies of non-Hermitian physics in non-equilibrium systems.