Quantum description of the optical response of charged monolayer-thick metallic patch nanoantennas

The optical response of small charged metallic nanodisks of one atomic monolayer thickness is analyzed under the excitation by an incident plane wave and by a localized pointlike dipole. Using the time-dependent density functional theory (TDDFT) and classical electrodynamical calculations we identify the bright and dark plasmon modes and study their evolution under external charging of the nanostructure. For neutral nanodisks, despite their monolayer thickness, the in-plane optical response, as obtained from TDDFT, is in agreement with classical electromagnetic results. The optical response for an incident wave polarized perpendicular to the nanostructure cannot be retrieved classically as it reflects a discrete energy structure of electronic levels. This latter situation appears most sensitive to external charging while the energy of the in-plane plasmon with dipolar character is nearly charge independent.J.A. and M.Z. acknowledge support from the Spanish Ministry of Economy and Competitiveness MINECO through project FIS2016-80174-P, as well as support from NIST Grant No. 70NANB15H32 of the US Department of Commerce. A.K.K acknowledges financial support from the project FIS2016-76617-P of MINECO. M.Z. also acknowledges the hospitality of the Institute des Sciences Moléculaires d’Orsay.Peer Reviewe