Low-Loss Plasmonics with Nanostructured Potassium and Sodium-Potassium Liquid Alloys

Alkali metals have low optical losses in the visibleto near-infrared(NIR) compared with noble metals. However, their high reactivity prohibitsthe exploration of their optical properties. Recently sodium (Na)has been experimentally demonstrated as a low-loss plasmonic material.Here we report on a thermo-assisted nanoscale embossing (TANE) techniquefor fabricating plasmonic nanostructures from pure potassium (K) andNaK liquid alloys. We show high-quality-factor resonances from K asnarrow as 15 nm in the NIR, which we attribute to the high materialquality and low optical loss. We further demonstrate liquid Na-Kplasmonics by exploiting the Na-K eutectic phase diagram. Ourstudy expands the material library for alkali metal plasmonics andliquid plasmonics, potentially enabling a range of new material platformsfor active metamaterials and photonic devices.

Automated summary

Alkali metals have low optical losses but high reactivity, limiting their exploration in optical properties. Sodium has been demonstrated as a low-loss plasmonic material. In this study, we used a thermo-assisted nanoscale embossing technique to fabricate plasmonic nanostructures from pure potassium and NaK liquid alloys. We achieved high-quality-factor resonances in the near-infrared region, expanding the material library for alkali metal plasmonics and liquid plasmonics.