Non-Hermitian Floquet phases with even-integer topological invariants in a periodically quenched two-leg ladder

TL;DR

This paper introduces a new class of non-Hermitian Floquet topological phases in a periodically quenched two-leg ladder system, characterized by even-integer invariants and edge modes, with a dynamical probe for these topological features.

Contribution

It presents an experimentally feasible model exhibiting rich non-Hermitian Floquet topological phases with even-integer invariants, expanding understanding of topology in driven open systems.

Findings

Emergence of non-Hermitian Floquet phases with even-integer invariants

Prediction of edge-localized zero- and π-quasienergy modes

Development of a dynamical probe for topological invariants

Abstract

Periodically driven non-Hermitian systems could possess exotic nonequilibrium phases with unique topological, dynamical and transport properties. In this work, we introduce an experimentally realizable two-leg ladder model subjecting to both time-periodic quenches and non-Hermitian effects, which belongs to an extended CII symmetry class. Due to the interplay between drivings and nonreciprocity, rich non-Hermitian Floquet topological phases emerge in the system, with each of them been characterized by a pair of even-integer topological invariants $(w_{0},w_{\pi})\in2\mathbb{Z}\times2\mathbb{Z}$. Under the open boundary condition, these invariants further predict the number of zero- and $\pi$-quasienergy modes localized around the edges of the system. We finally construct a generalized version of the mean chiral displacement, which could be employed as a dynamical probe to the topological invariants of non-Hermitian Floquet phases in the CII symmetry class. Our work thus introduces a new type of non-Hermitian Floquet topological matter, and further reveals the richness of topology and dynamics in driven open systems.