Optical Tuning of Non-Equilibrium Surface Plasmon Resonances in a Narrow-Gap Semiconductor Nanocavity

In photonics, the polaritonic nanocavity (PC) within the mid-infrared to terahertz region is pivotal in on-chip applications, spanning diverse domains such as bio-sensing and beyond-5G information processing. Nevertheless, the impediment posed by lattice vibrations' electrical neutrality restricts phononic PCs' active tuning through electro-optical methodologies. In response to this constraint, the potential of narrow-gap semiconductors is investigated, which is characterized by highly efficient optical carrier incubation capabilities to facilitate all-optical plasmonic PC tuning. Leveraging ultrafast nanoscopy, the temporal evolution of non-equilibrium plasmonic cavity modes is meticulously scrutinized in InSb nanosheets. These findings unveil that multi-valence band transitions engender substantial free carriers, culminating in optically tunable non-equilibrium plasmonic cavity modes with a rapid switching capability of less than 6 ps, affording facile 2π plasmonic phase control. This study substantiates the prospect that conventional III-V semiconductors offer a robust platform for tunable transient surface plasmon resonances, thereby paving the way for innovative integrated optical applications seamlessly adapting to established semiconductor technologies.