Gate-tunable near-field localization switching in black phosphorus via hybrid plasmonic excitation

Integrated photonics increasingly demands ultracompact, low-power, and highly tunable platforms for actively reconfigurable field control. Although black phosphorus (BP) provides strong electrostatic tunability and anisotropic plasmonic dispersion, practical BP plasmonic devices are often limited by lossy modes and out-of-plane excitation, restricting propagation and blurring dispersion-regime signatures at fixed frequencies. Here, we exploit a guided hybrid plasmonic excitation to realize abrupt, in-plane-compatible switching between localized and delocalized BP responses with small voltage variation. A Si/SiO2/Al/Si hybrid plasmonic waveguide produces a long-range slot–surface plasmon polariton (SPP) supermode; its plasmonic character efficiently excites a highly localized antisymmetric BP SPP, while its waveguide-like character preferentially couples to a weakly confined symmetric slab mode in a SiO2/BP/SiO2 region. By electrostatically tuning the BP Fermi level μ, we switch between these two regimes at f = 100 THz, as verified by Kubo-based conductivity modeling, dispersion analysis, near-field maps, and integrated |E|2 calculation. The resulting gate-reconfigurable field-localization transition adds a new control knob to 2D plasmonics and enables a scalable pathway to low-power, deeply subwavelength mid-IR switching and modulation within integrated photonic circuits.