Frustrated Non‐Hermitian Skin Effect in a Floquet Photonic System

ABSTRACT

The non‐Hermitian skin effect (NHSE) is conventionally understood as boundary accumulation of all bulk eigenmodes induced by nonreciprocal couplings. Here, we propose and experimentally demonstrate the frustrated NHSE in a Floquet photonic system, where this robust boundary localization is suppressed by a geometric scaling of the lattice couplings. Implementing a four‐step Floquet driving protocol, we engineer effective non‐reciprocal interactions from physically reciprocal couplings and dissipation. We reveal that a monotonic variation of lattice spacing induces a geometric localization that competes with the non‐reciprocity, driving a transition from skin modes to extended bulk modes. This phenomenon is experimentally demonstrated in a geometrically scaled optical waveguide array, where the edge localization in NHSE no longer occurs independently of the initial excitation location along the lattice. Our findings not only challenge the conventional understanding of the skin effect's robustness but also establish geometric scaling as a versatile design method for manipulating light in non‐conservative systems.