Gauge-Tunable Uniform Delocalization of Higher-Order Topological Photonic Modes

Higher-order topological photonic systems typically host corner states that are exponentially localized. Here we uncover a distinct regime of uniformly delocalized higher-order topological modes, emerging from the interplay of multiple spatially varying Dirac mass terms under chiral symmetry. These modes exhibit uniform large-area, sublattice-locked profiles that remain pinned at zero energy, independent of system size. Crucially, their internal phase admits a tunable gauge degree of freedom, enabling controlled reconfiguration without loss of topological protection. This dual combination of uniform delocalization and gauge-controlled tunability bridges the gap between scalable optical mode area and robust topological protection, and we further confirm these predictions experimentally in photonic crystals, observing excellent agreement with theory. Our scheme is directly applicable to photonic mode design and enables the realization of robust, large-area topological optical devices.