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

Gao, Zhi; Wildenborg, Aaron; Kocoj, Conrad A; Liu, Eric; Sheofsky, Caden; Rawashdeh, Abdelsalam; Qu, Hongwei; Guo, Peijun et al. · Nano Lett · 2023

basic_science · Level V

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Abstract

Alkali metals have low optical losses in the visible to near-infrared (NIR) compared with noble metals. However, their high reactivity prohibits the 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) technique for fabricating plasmonic nanostructures from pure potassium (K) and NaK liquid alloys. We show high-quality-factor resonances from K as narrow as 15 nm in the NIR, which we attribute to the high material quality and low optical loss. We further demonstrate liquid Na-K plasmonics by exploiting the Na-K eutectic phase diagram. Our study expands the material library for alkali metal plasmonics and liquid plasmonics, potentially enabling a range of new material platforms for active metamaterials and photonic devices.