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arXiv · 2409.16616

Broadband measurement of Feibelman's quantum surface response functions

Zeling Chen·Shu Yang·Zetao Xie·Jinbing Hu·Xudong Zhang·Yipu Xia·Yonggen Shen·Huirong Su·Maohai Xie·Thomas Christensen·Yi Yang
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Abstract

The Feibelman $d$-parameter, a mesoscopic complement to the local bulk permittivity, describes quantum optical surface responses for interfaces, including nonlocality, spill-in and-out, and surface-enabled Landau damping. It has been incorporated into the macroscopic Maxwellian framework for convenient modeling and understanding of nanoscale electromagnetic phenomena, calling for the compilation of a $d$-parameter database for interfaces of interest in nano-optics. However, accurate first-principles calculations of $d$-parameters face computational challenges, whereas existing measurements of $d$-parameters are scarce and restricted to narrow spectral windows. We demonstrate a general broadband ellipsometric approach to measure $d$-parameters at a gold--air interface across the visible--ultraviolet regimes. Gold is found to spill in and spill out at different frequencies. We also observe gold's Bennett mode, a surface-dipole resonance associated with a pole of the $d$-parameter, around 2.5 eV. Our measurements give rise to and are further validated by the passivity and Kramers--Kronig causality analysis of $d$-parameters. Our work advances the understanding of quantum surface response and may enable applications like enhanced electron field emission.

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Zeling Chen, Shu Yang, Zetao Xie, Jinbing Hu, Xudong Zhang, Yipu Xia, Yonggen Shen, Huirong Su, Maohai Xie, Thomas Christensen, Yi Yang. 2024-09-25. Broadband measurement of Feibelman's quantum surface response functions. https://arxiv.org/abs/2409.16616

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