Operation of Quantum Plasmonic Metasurfaces Using Electron Transport through Subnanometer Gaps

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Herein, we investigate the optical properties of quantum plasmonic metasurfaces composed of metallic nano-objects with subnanometer gaps according to the time-dependent density functional theory, a fully quantum mechanical approach. When the quantum and classical descriptions are compared, the transmission, reflection, and absorption rates of the metasurface exhibit substantial differences at shorter gap distances. The differences are caused by electron transport through the gaps of the nano-objects. The electron transport has profound influences for gap distances less-than or approximately 0.2 nm; that is, almost equal to half of the distance found in conventional gap plasmonics in isolated systems, such as metallic nanodimers. Furthermore, it is shown that the electron transport makes the plasmon features of the metasurface unclear and produces broad spectral structures in the optical responses. In particular, the reflection response exhibits rapid attenuation as the gap distance decreases, while the absorption response extends over a wide spectral range.