Topological edge states of plasmonic dark mode in one-dimensional split-ring nanochains

Topological plasmonics play a crucial role in advancing both fundamental physics and photonics applications. While research has primarily concentrated on topological edge states (TESs) associated with plasmon bright mode, the significant emission dissipation linked to these states limits enhancements in near-field performance. Conversely, TESs based on dark mode offer the promise of increased local field enhancement and reduced emission loss, potentially improving near-field characteristics. However, the influence of plasmon dark mode on TESs remains underexplored. This study employs symmetry breaking to activate dark mode in gold split-ring chains, realizing dark mode TESs. We report a near-field intensity enhancement of 595, an edge-to-bulk suppression ratio of 16.3, and a dephasing time of 13 fs in the split-ring chain, all outperforming bright mode TESs in nanodisk chains. Moreover, we achieve ultrafast switching between plasmon topological edge states and bulk states on the fs-nm scale using chirped laser pulses, enabling active control over state transitions. This work offers new insights into the applications of topological photonics.