Dispersive surface-response formalism to address nonlocality in extreme plasmonic field confinement

The surface-response formalism (SRF), where quantum surface-response corrections are incorporated into the classical electromagnetic theory via the Feibelman parameters, serves to address quantum effects in the optical response of metallic nanostructures. So far, the Feibelman parameters have been typically obtained from many-body calculations performed in the long-wavelength approximation, which neglects the nonlocality of the optical response in the direction parallel to the metal–dielectric interface, thus preventing to address the optical response of systems with extreme field confinement. To improve this approach, we introduce a dispersive SRF based on a general Feibelman parameter d ⊥(ω, k ‖), which is a function of both the excitation frequency, ω, and the wavenumber parallel to the planar metal surface, k ‖. An explicit comparison with time-dependent density functional theory (TDDFT) results shows that the dispersive SRF correctly describes the plasmonic response of planar and nonplanar systems featuring extreme field confinement. This work thus significantly extends the applicability range of the SRF, contributing to the development of computationally efficient semiclassical descriptions of light–matter interaction that capture quantum effects.MCIN/AEI/10.13039/501100011033/ (PID2019-107432GB-I00); Department of Education of the Basque Government (IT1526-22); “Investissements d’Avenir” LabEx PALM (ANR-10-LABX-0039-PALM)

Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.We acknowledge financial support from project IT1526–22 of the Department of Education of the Basque Government, and projects PID2019–107432GB-I00 and PID2022–139579NB-I00, funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”

Giant quantum electrodynamic effects on single SiV color centers in nanosized diamonds

Understanding and mastering quantum electrodynamics phenomena is essential to the development of quantum nanophotonics applications. While tailoring of the local vacuum field has been widely used to tune the luminescence rate and directionality of a quantum emitter, its impact on their transition energies is barely investigated and exploited. Fluorescent defects in nanosized diamonds constitute an attractive nanophotonic platform to investigate the Lamb shift of an emitter embedded in a dielectric nanostructure with high refractive index. Using spectral and time-resolved optical spectroscopy of single SiV defects, we unveil blue shifts (up to 80 meV) of their emission lines, which are interpreted from model calculations as giant Lamb shifts. Moreover, evidence for a positive correlation between their fluorescence decay rates and emission line widths is observed, as a signature of modifications not only of the photonic local density of states but also of the phononic one, as the nanodiamond size is decreased. Correlative light–electron microscopy of single SiVs and their host nanodiamonds further supports these findings. These results make nanodiamond-SiVs promising as optically driven spin qubits and quantum light sources tunable through nanoscale tailoring of vacuum-field fluctuations.We acknowledge the financial support from the French National Agency for Research, Région Nouvelle-Aquitaine, Idex Bordeaux (Research Program GPR Light), the EUR Light S&T (PIA3 Program, ANR-17-EURE0027), and the Laboratory for Transborder Cooperation LTC TRANS-LIGHT from University of Bordeaux and University of the Basque Country. B.L. acknowledges the Institut Universitaire de France. R.E. and J.A. acknowledge financial support from the Basque Government for consolidated groups of the Basque University (Grant IT 1526-22) and MCIN/AEI/10.13039/501100011033/(Grant PID2019-107432GB-I00).Peer reviewe

Quantum Many-Body Effects in the Optoelectronic Response of Plasmonic Nanostructures and their Coupling to Quantum Emitters

205 p.This thesis theoretically addresses the optoelectronic response of metallic nanoparticles (MNPs) as well as their coupling to quantum emitters (QEs). Nanometer-scale systems are considered where optical nonlinearity, nonlocality, or electron-transfer processes can all play an important role. To capture these quantum many-body effects, Time-Dependent Density Functional Theory (TDDFT) is used primarily, in combination with semiclassical models based on the Surface-Response Formalism (SRF) and classical calculations based on the Local-Response Approximation (LRA). We demonstrate that, at the nanometer scale, electron spill-out and surface-enabled Landau damping drastically influence the electromagnetic interaction between MNPs and QEs, which produce a redshift and broadening of plasmonic resonances not captured by classical theories. We show that these effects can be correctly described by the semiclassical SRF, in particular when one considers the nonlocal response in the direction parallel to the metal surface. In addition, we predict that the hybridization between the electronic states of the QE and those of the MNPs drastically modifies the optical response of the coupled system in situation involving subnanometric distances, since the exciton in the QE is found to be quenched due to electronic coupling. This quenching dramatically influences the frequency and the width of the optical resonances sustained by the coupled structure. Finally, we demonstrate that the electromagnetic coupling of a QE to a spherical MNP can also affect the nonlinear optical response of the system, enabling otherwise-forbidden second-harmonic generation (SHG)

Electronic exciton-plasmon coupling in a nanocavity beyond the electromagnetic interaction picture

The optical response of a system formed by a quantum emitter and a plasmonic gap nanoantenna is theoretically addressed within the frameworks of classical electrodynamics and the time-dependent density functional theory (TDDFT). A fully quantum many-body description of the electron dynamics within TDDFT allows for analyzing the effect of electronic coupling between the emitter and the nanoantenna, usually ignored in classical descriptions of the optical response. We show that the hybridization between the electronic states of the quantum emitter and those of the metallic nanoparticles strongly modifies the energy, the width, and the very existence of the optical resonances of the coupled system. We thus conclude that the application of a quantum many-body treatment that correctly addresses charge-transfer processes between the emitter and the nanoantenna is crucial to address complex electronic processes involving plasmon–exciton interactions directly impacting optoelectronic applications.A.B. thanks the hospitality and nice atmosphere at the Institut des Sciences Moléculaires d’Orsay, France, and also the Department of Education of the Basque Government for a predoctoral fellowship (PRE2017_1_0267). A.B., R.E., and J.A. acknowledge project PID2019-107432GB-I00 from Spanish MICINN and project PI2017-30 and grant IT1164-19 for consolidated groups of the Basque University system from the Department of Education of the Basque Government. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 861950, project POSEIDON.Peer reviewe

Nonlinear optical response of a plasmonic nanoantenna to circularly polarized light: Rotation of multipolar charge density and near-field spin angular momentum inversion

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.We acknowledge financial support from project IT1526–22 of the Department of Education of the Basque Government, and projects PID2019–107432GB-I00 and PID2022–139579NB-I00, funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”.Peer reviewe

Research data supporting "Electronic Exciton-Plasmon Coupling in a Nanocavity Beyond the Electromagnetic Interaction Picture"

We include the dataset corresponding to the figures of the paper "Electronic Exciton−Plasmon Coupling in a Nanocavity Beyond the Electromagnetic Interaction Picture" by A. Babaze, R. Esteban, A.G. Borisov, and J. Aizpurua, published in the journal Nano Letters, with DOI: 10.1021/acs.nanolett.1c03202 . The set includes data to generate: optical spectra, charge and current density maps, projected density of electronic states, and plots in the paper.Peer reviewe

Research data supporting "Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion"

We include the dataset corresponding to the figures of the paper "Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion" by M. Quijada, A. Babaze, J. Aizpurua, and A.G. Borisov, published in the journal ACS Photonics, with DOI: 10.1021/acsphotonics.3c00783 . The set includes data to generate: optical spectra, charge density maps, time evolution of multipolar moments, and all the plots in the paper.Peer reviewe

Influence of “electronic” exciton–plasmon coupling in the optical response of (sub)-nanometric metallic junctions

Resumen del trabajo presentado a la Conferencia Española de Nanofotónica (CEN), celebrada en Vigo del 20 al 22 de septiembre de 2021.Project PID2019-107432GB-I00 (Spanish MICINN). Predoctoral Fellowship No. PRE2017_1_0267 and Grant IT1164-19 (Department of Education of the Basque Government). Project H2020-FET Open ‘POSEIDON’ (European Commision).Peer reviewe

Second-harmonic generation from a quantum emitter coupled to a metallic nanoantenna

We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.A.B., R.E., and J.A. acknowledge the National Project FIS2016-80174-P from the MICINN and Project PI2017-30 and Grant No. IT1164-19 for research groups of the Basque University system from the Department of Education of the Basque Government. A.B also thanks Dr. Garikoitz Aguirregabiria for valuable technical advice on the TDDFT simulations of metallic nanoparticles and the Department of Education of the Basque Government for a predoctoral fellowship (Grant No. PRE2017_1_0267).Peer reviewe