Observation of photonic asymmetric topological corner modes driven by periodically staggered onsite edge potentials

Controlling topological modes in photonic systems remains a fundamental challenge, as conventional approaches rely on global lattice modifications and lack topological phase engineering of the induced non-trivial states. Here, we reveal that staggered onsite edge potential (SOEP) modulation breaks mirror symmetry in folded edge states, inducing edge-confined Wannier function deviations and thus driving edge bands into distinct topological phases. The emergence of resulting higher-order localized modes is further confirmed. Notably, the hosted corner modes are SOEP-selective, depending on the deviation direction of the Wannier function. Using spoof surface plasmon polariton photonic crystals, we experimentally confirm two SOEP-driven evolution regimes: symmetric evolution enabling corner-mode pumping between adjacent corners and asymmetric evolution restricting corner modes to negative potentials. These results demonstrate spatial control over corner states, linking edge potential engineering to higher-order topology. Our study paves the way for manipulating the band structure and modeling topological phases of photonic states.