Topological phase singularities enabled by hybrid polaritons for robust ultra-sensitive sensing

High-precision optical sensing is fundamental to applications in biomedicine, environmental monitoring, and integrated photonics. A key challenge at the nanoscale is to combine strong field confinement with high spectral sensitivity, which conventional resonators or plasmonic platforms struggle to achieve due to broad linewidths and fabrication sensitivity. We propose a hybrid polaritonic structure where localized surface plasmon polaritons coherently couple to a Tamm plasmon polariton, giving rise to topological phase singularities. These singularities occur at near-zero reflectance, producing abrupt phase transitions and divergent phase sensitivity that far exceed amplitude-based sensing schemes. The platform further exhibits robustness against structural perturbations, such as positional shifts of embedded plasmonic defects. Our results demonstrate a compact, tunable, and topologically protected mechanism for refractive-index sensing, surpassing conventional surface plasmon resonance sensors and opening a route toward singularity-enhanced photonic devices.