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Floquet non-Bloch formalism for a non-Hermitian ladder: From theoretical framework to topolectrical circuits

Koustav Roy1,*,†, Dipendu Halder1,*,‡, Koustabh Gogoi2, B. Tanatar3,§, and Saurabh Basu1

  • *These authors contributed equally to this work.
  • †Contact author: koustav.roy@iitg.ac.in
  • ‡Contact author: h.dipendu@iitg.ac.in
  • §Contact author: tanatar@fen.bilkent.edu.tr
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Phys. Rev. Research 7, 043331 – Published 24 December, 2025

DOI: https://doi.org/10.1103/s3b6-wz16

Abstract

Periodically driven systems intertwined with non‐Hermiticity open a rich arena for topological phases that transcend conventional Hermitian limits. The physical significance of these phases hinges on obtaining the topological invariants that restore the bulk‐boundary correspondence, a task well explored for static non-Hermitian (NH) systems, while it remains elusive for the driven scenario. Here, we address this problem by constructing a generalized Floquet non‐Bloch framework that analytically captures the spectral and topological properties of time-periodic NH systems. Employing a high-frequency Magnus expansion, we analytically derive an effective Floquet Hamiltonian and formulate the generalized Brillouin zone for a periodically driven quasi-one-dimensional system, namely, the Creutz ladder with a staggered complex potential. Our study demonstrates that the skin effect remains robust (despite the absence of nonreciprocal hopping) across a broad range of driving parameters, and is notably amplified in the low-frequency regime due to emergent longer-range couplings. We further employ a symmetric time frame approach that generates chiral-partner Hamiltonians, whose invariants, when appropriately combined, account for the full edge-state structure. To substantiate the theoretical framework, we propose a topolectrical circuit (TEC) that serves as a viable experimental setting. Apart from capturing the skin modes, the proposed TEC design faithfully reproduces the presence of distinct Floquet edge states, as revealed through the voltage and impedance profiles, respectively. Thus, our work not only offers a theoretical framework for exploring NH-driven systems but also provides an experimentally feasible TEC architecture for realizing these phenomena stated above in a laboratory.

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Phys. Rev. Research 7, 043331– Published 24 December, 2025
  • Received 1 August 2025
  • Accepted 24 November 2025
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