Broadband measurement of Feibelman's quantum surface response functions
Abstract
The Feibelman -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 -parameter database for interfaces of interest in nano-optics. However, accurate first-principles calculations of -parameters face computational challenges, whereas existing measurements of -parameters are scarce and restricted to narrow spectral windows. We demonstrate a general broadband ellipsometric approach to measure -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 -parameter, around 2.5 eV. Our measurements give rise to and are further validated by the passivity and Kramers--Kronig causality analysis of -parameters. Our work advances the understanding of quantum surface response and may enable applications like enhanced electron field emission.
Keywords
Cite
@article{arxiv.2409.16616,
title = {Broadband measurement of Feibelman's quantum surface response functions},
author = {Zeling Chen and Shu Yang and Zetao Xie and Jinbing Hu and Xudong Zhang and Yipu Xia and Yonggen Shen and Huirong Su and Maohai Xie and Thomas Christensen and Yi Yang},
journal= {arXiv preprint arXiv:2409.16616},
year = {2024}
}