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

Abstract

Abstract 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.