Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms

Domenico De Ceglia, Michael Scalora, Maria A. Vincenti, Salvatore Campione, Kyle Kelley, Evan L. Runnerstrom, Jon Paul Maria, Gordon A. Keeler, Ting S. Luk

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Abstract

Optical nonlocalities are elusive and hardly observable in traditional plasmonic materials like noble and alkali metals. Here we report experimental observation of viscoelastic nonlocalities in the infrared optical response of epsilon-near-zero nanofilms made of low-loss doped cadmium-oxide. The nonlocality is detectable thanks to the low damping rate of conduction electrons and the virtual absence of interband transitions at infrared wavelengths. We describe the motion of conduction electrons using a hydrodynamic model for a viscoelastic fluid, and find excellent agreement with experimental results. The electrons' elasticity blue-shifts the infrared plasmonic resonance associated with the main epsilon-near-zero mode, and triggers the onset of higher-order resonances due to the excitation of electron-pressure modes above the bulk plasma frequency. We also provide evidence of the existence of nonlocal damping, i.e., viscosity, in the motion of optically-excited conduction electrons using a combination of spectroscopic ellipsometry data and predictions based on the viscoelastic hydrodynamic model.

Original languageEnglish (US)
Article number9335
JournalScientific reports
Volume8
Issue number1
DOIs
StatePublished - Dec 1 2018

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De Ceglia, D., Scalora, M., Vincenti, M. A., Campione, S., Kelley, K., Runnerstrom, E. L., Maria, J. P., Keeler, G. A., & Luk, T. S. (2018). Viscoelastic optical nonlocality of low-loss epsilon-near-zero nanofilms. Scientific reports, 8(1), [9335]. https://doi.org/10.1038/s41598-018-27655-z