Low-Loss Plasmonics with Nanostructured Potassium and Sodium–Potassium Liquid Alloys
Zhi Gao, Aaron J. Wildenborg, Conrad A. Kocoj, Eric Liu, Caden Sheofsky, Abdelsalam Rawashdeh, Hongwei Qu, Peijun Guo, Jae Yong Suh, Ankun Yang
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.