CC BY
11PH-I-2
Linear and nonlinear optical responses of plasmonic metasurface with sub-nm gaps
T. Takeuchi1, M. Noda1, K. Yabana1
University of Tsukuba, Center for Computational Sciences, Tsukuba, Japan
A plasmonic metasurface in which metallic nano-objects are periodically placed on a plane has attracted substantial attention in terms of its exotic optical characteristics [1]. Although investigations have been devoted mostly to metasurfaces with wavelength or sub-wavelength gap distances between constituent nano-objects, experimental studies have been reported recently for periodic structures with much smaller gap distances, reaching to sub-nm [2]. In isolated systems with a sub-nm gap such as a metallic nanodimer, it has been revealed that optical properties show substantial differences between theoretical descriptions using classical and quantum theories in the linear response regime [3]. The difference becomes remarkable for gap distances less than 0.4 nm [4] where the quantum tunneling across the gap becomes sizable. Furthermore, very recently, nonlinear responses of plasmonic metasurfaces with sub-nm gaps have been attracting attention since large third-order nonlinear susceptibility has been observed [5].
We theoretically and numerically investigate the plasmonic metasurface with sub-nm gaps in both linear and nonlinear response regimes. To take into account quantum mechanical effects in the analysis, we employ time-dependent density functional theory (TDDFT) treating the constituent nano-particles by a jellium model. SALMON (https://salmon-tddft.jp/) developed by our group [6] has been used for the numerical calculation. We will show transmission, reflection, and absorption rates of the metasurface for a weak incident field to elucidate the electron transport effect through the sub-nm gaps. We also show third-order harmonic generations to explore effects of the electron transport on their nonlinear optical response.
References
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[3] W. Zhu, R. Esteban, A. G. Borisov, J. J. Baumberg, P. Nordlander, H. J. Lezec1, J. Aizpurua, and K. B. Crozier, Nat. Commun. 7, 11495 (2016).
[4] K. J. Savage, M. M. Hawkeye, R. Esteban, A. G. Borisov, J. Aizpurua, and J. J. Baumberg, Nature 491, 574 (2012).
[5] L. S. Menezes, L. H. Acioli, M. Maldonado, J. Naciri, N. Charipar, J. Fontana, D. Rativa, C. B. Araújo, and A. S. L. Gomes, J. Opt. Soc. Am. B 36, 1485 (2019).
[6] M. Noda, S. A. Sato, Y. Hirokawa, M. Uemoto, T. Takeuchi, S. Yamada, A. Yamada, Y. Shinohara, M. Yamaguchi, K. Iida, I. Floss, T. Otobe, K.-M. Lee, K. Ishimura, T. Boku, G. F. Bertsch, K. Nobusada, K. Yabana, Comput. Phys. Comm 235, 356 (2019).
