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  • Letter
  • Open Access

Topology and edge modes surviving criticality in non-Hermitian Floquet systems

Longwen Zhou*

  • College of Physics and Optoelectronic Engineering, Ocean University of China, Qingdao 266100, China; Qingdao Key Laboratory of Advanced Optoelectronics, Qingdao 266100, China; and Engineering Research Center of Advanced Marine Physical Instruments and Equipment of MOE, Qingdao 266100, China

  • *Contact author: zhoulw13@u.nus.edu
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Phys. Rev. Research 8, L022026 – Published 11 May, 2026

DOI: https://doi.org/10.1103/x9kx-v9d2

Abstract

The discovery of critical points that can host quantized nonlocal order parameters and degenerate edge modes relocates the study of symmetry-protected topological phases (SPTs) to gapless regions. In this Letter, we reveal gapless SPTs (gSPTs) in systems tuned out of equilibrium by periodic drivings and non-Hermitian couplings. Focusing on one-dimensional models with sublattice symmetry, we introduce winding numbers by applying the Cauchy's argument principle to generalized Brillouin zone, yielding unified topological characterizations and bulk-edge correspondence both in gapped phases and at gapless critical points. The theory is demonstrated in a broad class of Floquet bipartite lattices, unveiling unique topological criticality of non-Hermitian Floquet origin. Our findings identify gSPTs in driven open systems and uncover robust topological edge modes at phase transitions beyond equilibrium.

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Phys. Rev. Research 8, L022026– Published 11 May, 2026
  • Received 5 December 2025
  • Accepted 25 April 2026
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