Extreme mid-infrared field enhancement and anapoles in high-index plasmonic metamaterials

Zoltan Sztranyovszky; Nicolas Spiesshofer; Caleb Todd; Rakesh Arul; Yeeun Roh; Rohit Chikkaraddy; Jeremy J. Baumberg; Angela Demetriadou

arXiv · 2606.19114

Extreme mid-infrared field enhancement and anapoles in high-index plasmonic metamaterials

Zoltan Sztranyovszky·Nicolas Spiesshofer·Caleb Todd·Rakesh Arul·Yeeun Roh·Rohit Chikkaraddy·Jeremy J. Baumberg·Angela Demetriadou

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Abstract

High-refractive-index materials underpin a wide range of optical technologies, including communications, imaging, lasers, and integrated photonic systems. Here, we demonstrate a self-assembled metamaterial platform based on gold nanoparticle aggregates with nanometer-scale gaps exhibit remarkably high effective refractive indices exceeding 15 in the mid-infrared regime, while simultaneously producing gap-field enhancements of at least two-orders of magnitude. This combination of high refractive index and extreme field enhancement enables exceptionally strong light-matter interactions. We demonstrate this by designing a compact high-index metamaterial device supporting an anapole, which further enhances the nanogap field. By placing quantum emitters with terahertz transitions inside the plasmonic gaps, we show a stimulated-emission response enhanced by at least three orders of magnitude, highlighting applications in non-linear optics, frequency up-conversion and vibrational strong coupling.

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Zoltan Sztranyovszky, Nicolas Spiesshofer, Caleb Todd, Rakesh Arul, Yeeun Roh, Rohit Chikkaraddy, Jeremy J. Baumberg, Angela Demetriadou. 2026-06-17. Extreme mid-infrared field enhancement and anapoles in high-index plasmonic metamaterials. https://arxiv.org/abs/2606.19114

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