2024 |
Aguillon, F., & Borisov, A. G. (2024). Nonlinear Response of Nanostructured Graphene to Circularly Polarized Light. J. Phys. Chem. C, 128(39), 16576–16587.
Résumé: Using the tight-binding description of graphene and the time-dependent density matrix approach, we theoretically address the nonlinear response of plasmonic graphene nanostructures to the circularly polarized light. The intensity and polarization of emitted harmonics depend on the symmetry of the system and can be analyzed by applying Neumann’s principle. We find that for the nanoflakes comprising thousands of carbon atoms, it is the symmetry of the carbon atom arrangement on the atomic scale that determines the nonlinear response. Therefore, it might be very different from the nonlinear response predicted using the macroscopic geometry. For the compound systems made of several nanoflakes, we reveal the role of the near-field interactions in intensity and circular polarization states of emitted harmonics. Finally, we show that symmetry break by, e.g., lattice defects strongly affects the nonlinear response of graphene nanoflakes to the circularly polarized light. Our work extends the theoretical studies of the nonlinear optical properties of graphene nanomaterials toward spin-carrying light beams.
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Borisov, A. G. (2024). Model description of electron transfer between PTCDA molecule and metal surface upon molecular adsorption and STM manipulation. Phys. Rev. B, 110, 075413.
Résumé: The coupling between the molecule-localized electronic states and continuum of the electronic states of the metal surface is of paramount importance for adsorption dynamics, surface reactivity, as well as for the electron- and photon-induced processes at metal surfaces. Here, using the model one-active-electron description and wave-packet propagation approach, we study the resonant electron transfer between the perylene-tetracarboxylic-dianhydride (PTCDA) molecule and metal substrate from 0.5 nm separations down to the adsorption distances. We also address the situation where the molecule is lifted up from the substrate using the scanning tunneling microscope. A detailed comparison with the large amount of available experimental data and ab initio calculations allows us to discuss the validity of the method and the main robust effects driving the lifetimes of molecule-localized states that it reveals. Thus we show that the symmetry of molecule-localized states strongly impacts the dependence of the electron transfer rates on the metal band structure and molecule-surface distance. In addition, in full agreement with recent experimental data on scanning tunneling microscopy manipulation where an adsorbed molecule is lifted into the vertical geometry, we find an order of magnitude reduction of the adsorbate-substrate coupling.
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2023 |
Aguillon, F., & Borisov, A. G. (2023). Atomic-Scale Defects Might Determine the Second Harmonic Generation from Plasmonic Graphene Nanostructures. J. Phys. Chem. Lett., 14, 238–244.
Résumé: In this work, we theoretically investigate the impact of the atomic scale lattice imperfections of graphene nanoflakes on their nonlinear response enhanced by the resonance between an incident electromagnetic field and localized plasmon. As a case study, we address the second harmonic generation from graphene plasmonic nanoantennas of different symmetries with missing carbon atom vacancy defects in the honeycomb lattice. Using the many-body time-dependent density matrix approach, we find that one defect in the nanoflake comprising over five thousand carbon atoms can strongly impact the nonlinear hyperpolarizability and override the symmetry constraints. The effect reported here cannot be captured using the relaxation time approximation within the quantum or classical framework. Results obtained in this work have thus important implications for the design of nonlinear graphene devices.
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Babaze, A., Neuman, T., Esteban, R., Aizpurua, J., & Borisov, A. G. (2023). Dispersive surface-response formalism to address nonlocality in extreme plasmonic field confinement. Nanophotonics, 12(16), 3277–3289.
Résumé: 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.
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Le Moal, S., Krieger, I., Kremring, R.: W., S. Yang, X.: Soubatch, S, Tautz, F. S., Silly, M., Borisov, A. G., Sokolowski, M., & Le Moal, E. (2023). Core-Level Binding Energy Shifts in Ultrathin Alkali-Halide Films on Metals: KCl on Ag(100). J. Phys. Chem. C, 127(50), 24253–24265.
Résumé: We present an experimental and theoretical analysis of the core-level binding energy shifts in metal-supported ultrathin KCl films, i.e., a case from a broader class of fewatom-thick, wide-bandgap insulating layers that is increasingly used in nanosciences and nanotechnologies. Using synchrotron-based high-resolution photoemission spectroscopy (HRPES) measurements, we identify the different contributions to the core-level binding energy shifts for the Cl– anions and K+ cations of two to three atomic layer-thick KCl films grown on Ag(100). The distances of the Cl– and K+ ions of the first two atomic layers of the KCl film from the metal substrate are determined from normal incidence X-ray standing wave measurements. We also calculate the core-level binding energy shifts using an analytical electrostatic model and find that the theoretical results are in agreement with the experimental HRPES results only when polarization and substrateinduced image charge effects are taken into account. Finally, our results evidence the effect of the third atomic layer of the KCl film, which partially covers and screens the first two atomic layers of KCl wetting the metal substrate.
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Quijada, M., Babaze, A., Aizpurua, J., & Borisov, A. G. (2023). Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion. ACS Photon., 10(11), 3963–3975.
Résumé: 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.
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2022 |
Aguillon, F., Marinica, D. C., & Borisov, A. G. (2022). Atomic-scale control of plasmon modes in graphene nanoribbons. Phys. Rev. B, 105, L081401.
Résumé: We address the possibility of atomic-scale control of the plasmon modes of graphene nanostructures. Using the time-dependent many-body approach we show that for the zigzag and armchair nanoribbons, the single carbon atom vacancy results in “on” and “off” switching of the longitudinal plasmon modes or in a change of their frequency. The effect stems from the robust underlying physical mechanism based on the strong scattering of the two-dimensional (2D) electrons on the vacancy defects in graphene lattice. Thus our findings establish a platform for optical response engineering or sensing in 2D materials.
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Babaze, A., Ogando, E., Stamatopoulou, P. E., Tserkezis, C., Mortensen, N. A., Aizpurua, J., Borisov, A. G., & Esteban, R. (2022). Quantum surface effects in the electromagnetic coupling between a quantum emitter and a plasmonic nanoantenna: time-dependent density functional theory vs. semiclassical Feibelman approach. Opt. Express, 30(12), 21159–21183.
Résumé: We use time-dependent density functional theory (TDDFT) within the jellium model to study the impact of quantum-mechanical effects on the self-interaction Green’s function that governs the electromagnetic interaction between quantum emitters and plasmonic metallic nanoantennas. A semiclassical model based on the Feibelman parameters, which incorporates quantum surface-response corrections into an otherwise classical description, confirms surface-enabled Landau damping and the spill out of the induced charges as the dominant quantum mechanisms strongly affecting the nanoantenna–emitter interaction. These quantum effects produce a redshift and broadening of plasmonic resonances not present in classical theories that consider a local dielectric response of the metals. We show that the Feibelman approach correctly reproduces the nonlocal surface response obtained by full quantum TDDFT calculations for most nanoantenna–emitter configurations. However, when the emitter is located in very close proximity to the nanoantenna surface, we show that the standard Feibelman approach fails, requiring an implementation that explicitly accounts for the nonlocality of the surface response in the direction parallel to the surface. Our study thus provides a fundamental description of the electromagnetic coupling between plasmonic nanoantennas and quantum emitters at the nanoscale.
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Koval, N. E., Sánchez-Portal, D., Borisov, A. G., & Díez Muiño, R. (2022). Time-dependent density functional theory calculations of electronic friction in non-homogeneous media. Phys. Chem. Chem. Phys., 24(34), 20239–20248.
Résumé: The excitation of low-energy electron–hole pairs is one of the most relevant processes in the gas–surface interaction. An efficient tool to account for these excitations in simulations of atomic and molecular dynamics at surfaces is the so-called local density friction approximation (LDFA). The LDFA is based on a strong approximation that simplifies the dynamics of the electronic system: a local friction coefficient is defined using the value of the electronic density for the unperturbed system at each point of the dynamics. In this work, we apply real-time time-dependent density functional theory to the problem of the electronic friction of a negative point charge colliding with spherical jellium metal clusters. Our non-adiabatic, parameter-free results provide a benchmark for the widely used LDFA approximation and allow the discussion of various processes relevant to the electronic response of the system in the presence of the projectile.
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Peña Román, R. J., Bretel, R., Pommier, D., Parra López, L. E., Lorchat, E., Boer-Duchemin, E., Dujardin, G., Borisov, A. G., Zagonel, L. F., Schull, G., Berciaud, S., & Le Moal, E. (2022). Tip-Induced and Electrical Control of the Photoluminescence Yield of Monolayer WS2. Nano Lett., 22(23), 9244–9251.
Résumé: The photoluminescence (PL) of monolayer tungsten disulfide (WS2) is locally and electrically controlled using the nonplasmonic tip and tunneling current of a scanning tunneling microscope (STM). The spatial and spectral distribution of the emitted light is determined using an optical microscope. When the STM tip is engaged, short-range PL quenching due to near-field electromagnetic effects is present, independent of the sign and value of the bias voltage applied to the tip–sample tunneling junction. In addition, a bias-voltage-dependent long-range PL quenching is measured when the sample is positively biased. We explain these observations by considering the native n-doping of monolayer WS2 and the charge carrier density gradients induced by electron tunneling in micrometer-scale areas around the tip position. The combination of wide-field PL microscopy and charge carrier injection using an STM opens up new ways to explore the interplay between excitons and charge carriers in two-dimensional semiconductors.
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Rosławska, A., Neuman, T., Doppagne, B., Borisov, A. G., Romeo, M., Scheurer, F., Aizpurua, J., & Schull, G. (2022). Mapping Lamb, Stark, and Purcell Effects at a Chromophore-Picocavity Junction with Hyper-Resolved Fluorescence Microscopy. Phys. Rev. X, 12, 011012.
Résumé: The interactions of the excited states of a single chromophore with static and dynamic electric fields spatially varying at the atomic scale are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extension of the fields confined at the apex of a scanning tunneling microscope tip is smaller than that of the molecular exciton, a property used to generate fluorescence maps of the chromophore with intramolecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the picocavity junction formed by the chromophore, the tip, and the substrate reveal the key role played by subtle variations of Purcell, Lamb, and Stark effects. They also demonstrate that hyper-resolved fluorescence maps of the line shift and linewidth of the excitonic emission can be understood as images of the static charge redistribution upon electronic excitation of the molecule and as the distribution of the dynamical charge oscillation associated with the molecular exciton, respectively.
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2021 |
Aguilar-Galindo, F., Borisov, A. G., & Díaz-Tendero, S. (2021). Ultrafast Dynamics of Electronic Resonances in Molecules Adsorbed on Metal Surfaces: A Wave Packet Propagation Approach. J. Chem. Theory Comput., 17(2), 639–654.
Résumé: We present a wave packet propagation-based method to study the electron dynamics in molecular species in the gas phase and adsorbed on metal surfaces. It is a very general method that can be employed to any system where the electron dynamics is dominated by an active electron and the coupling between the discrete and continuum electronic states is of importance. As an example, one can consider resonant molecule–surface electron transfer or molecular photoionization. Our approach is based on a computational strategy allowing incorporating ab initio inputs from quantum chemistry methods, such as density functional theory, Hartree–Fock, and coupled cluster. Thus, the electronic structure of the molecule is fully taken into account. The electron wave function is represented on a three-dimensional grid in spatial coordinates, and its temporal evolution is obtained from the solution of the time-dependent Schrödinger equation. We illustrate our method with an example of the electron dynamics of anionic states localized on organic molecules adsorbed on metal surfaces. In particular, we study resonant charge transfer from the π* orbitals of three vinyl derivatives (acrylamide, acrylonitrile, and acrolein) adsorbed on a Cu(100) surface. Electron transfer between these lowest unoccupied molecular orbitals and the metal surface is extremely fast, leading to a decay of the population of the molecular anion on the femtosecond timescale. We detail how to analyze the time-dependent electronic wave function in order to obtain the relevant information on the system: the energies and lifetimes of the molecule-localized quasistationary states, their resonant wavefunctions, and the population decay channels. In particular, we demonstrate the effect of the electronic structure of the substrate on the energy and momentum distribution of the hot electrons injected into the metal by the decaying molecular resonance.
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Aguilar-Galindo, F., Zapata-Herrera, M., Díaz-Tendero, S., Aizpurua, J., & Borisov, A. G. (2021). Effect of a Dielectric Spacer on Electronic and Electromagnetic Interactions at Play in Molecular Exciton Decay at Surfaces and in Plasmonic Gaps. ACS Photon., 8(12), 3495–3505.
Résumé: The deposition of individual molecules, molecular networks, and molecular layers at surfaces is at the core of surface reactivity, energy harvesting, molecular electronics, and (single) photon sources. Yet, strong adsorbate–substrate interaction on metallic surfaces quenches the excited molecular states and harms many practical applications. Here, we theoretically address the role of a NaCl ionic crystal spacer layer in decoupling an adsorbate from the substrate and therefore changing the interplay between the competing decay channels of an excited molecule driven by electronic and electromagnetic interactions. A quantitative assessment of the corresponding decay rates allows us to establish the minimum thickness of the spacer required for the observation of molecular luminescence from the junction of a scanning tunneling microscope. Our work provides a solid quantitative theoretical basis relevant for several fields of nanotechnology where engineering of ionic crystal spacers allows for adsorbate charge manipulation, reactivity, and photon emission in nanocavities.
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Aguilar-Galindo, F., Borisov, A. G., & Díaz-Tendero, S. (2021). Unveiling the Anisotropic Behavior of Ultrafast Electron Transfer at the Metal/Organic Interface. Appl. Surf. Sci., 554, 149311.
Résumé: Ultrafast electron transfer between adsorbed organic molecules and metal substrates is studied. In particular, the dynamics of the active electron in the nitroethylene anion/metal-copper surface system has been followed in real time using a wave packet propagation approach, allowing an intuitive analysis of the decay of molecule-localized electronic resonances. We find that the strong coupling with the metal substrate leads to an extremely short lifetime (fs) of the molecular resonance. Comparison between the free-electron metal, Cu(100), and Cu(111) surfaces demonstrates that the electronic band structure of the substrate and the shape of the decaying molecular orbital lead to a highly marked anisotropy of the metal continuum states populated by resonant electron transfer from the adsorbate. This finding points at possible anisotropy effects in adsorbate-adsorbate interactions and it is of particular importance in molecular self assembly at metal surfaces, thus opening the way to a rational design of hybrid metal/organic interfaces with tailored electronic properties.
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Aguillon, F., Marinica, D. C., & Borisov, A. G. (2021). Plasmons in Graphene Nanostructures with Point Defects and Impurities. J. Phys. Chem. C, 125(39), 21503–21510.
Résumé: The exceptional electronic and optical properties of graphene are harmed by the unavoidable imperfections of the lattice resulting from mechanical or electronic interaction with the environment. Using a time-dependent approach, we theoretically address the sensitivity of the plasmon modes of graphene nanoflakes to the presence of point vacancy defects and substitutional impurities. We find that the fractions of the defects as low as 10–3 from the total number of carbon atoms in an ideal nanoflake lead to strong broadening of the plasmon resonance in the optical absorption spectrum. In addition to this effect resulting from the elastic and inelastic processes associated with defect-induced scattering and modification of the electronic structure of graphene, we also observe and explain the vacancy and impurity-induced shifts of the plasmon energy. Our work extends the in depth theoretical studies of the optical properties of graphene nanomaterials toward practical situations of nonideal 2D lattices.
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Babaze, A., Esteban, R., Borisov, A. G., & Aizpurua, J. (2021). Electronic Exciton−Plasmon Coupling in a Nanocavity Beyond the Electromagnetic Interaction Picture. Nano Lett., 21(19), 8466–8473.
Résumé: 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.
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Roslawska, A., Neuman, T., Doppagne, B., Borisov, A. G., Romeo, M., Scheurer, F., Aizpurua, J., & Schull, G. (2021). Mapping Lamb, Stark and Purcell effects at a chromophore-picocavity junction with hyper-resolved fluorescence microscopy. Retrieved January 9, 2025, from https://arxiv.org/abs/2107.01072
Résumé: The interactions between the excited states of a single chromophore with static and dynamic electric fields confined to a plasmonic cavity of picometer dimensions are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extensions of the confined fields are smaller than the one of the molecular exciton, a property that is used to generate fluorescence maps of the chromophores with intra-molecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the chromophore-picocavity junction are able to reproduce and interpret these hyper-resolved fluorescence maps, and reveal the key role played by subtle variations of Purcell, Lamb and Stark effects at the chromophore-picocavity junction.
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2020 |
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Aguilar-Galindo, F., Díaz-Tendero, S., & Borisov, A. G. (2020). Resonant anionic states of organic molecules adsorbed on metal surfaces. In Journal of Physics: Conference Series (Vol. 1412, 202015).
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Aguillon, F., Marinica, D. C., & Borisov, A. G. (2020). Molecule Detection with Graphene Dimer Nanoantennas. J. Phys. Chem. C, 124(51), 28210–28219.
Résumé: Using the tight binding description of the electronic structure of graphene and a time-dependent quantum approach, we address the vibrational excitation of molecules in the near field of a graphene nanoantenna. The possibility of tuning the graphene plasmon frequency by electrostatic doping allows an efficient resonant excitation of the infrared (IR)-active vibrational modes via the coupling between the molecular dipole and plasmon near field. We show that for the carbon monoxide CO molecules placed in the gap of a dimer antenna formed by the 20 nm size graphene patches, an excitation of the υ=1←0 transition leads to a distinct molecular signature in the IR absorption spectrum of the system. A very small number of molecules down to a single molecule placed in the antenna gap can thus be detected. Along with IR-active vibrations, the inhomogeneity of the plasmonic near field allows vibrational excitation of IR-inactive molecules via molecular quadrupole. The resonant excitation of the N2 molecule vibration is thus observed in the calculated absorption spectra, albeit the molecule signature is essentially smaller than for the CO molecule. Obtained with molecules described on the ab initio quantum chemistry level, our results provide quantitative insights into the performance of graphene nanoflakes and their dimers for molecular sensing.
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Babaze, A., Esteban, R., Aizpurua, J., & Borisov, A. G. (2020). Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna. ACS Photonics, 7(3), 701–713.
Résumé: 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.
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Cao, S., Zapata-Herrera, M., Campos, A., Le Moal, E., Marguet, S., Dujardin, G., Kociak, M., Aizpurua, J., Borisov, A. G., & Boer-Duchemin, E. (2020). Probing the Radiative Electromagnetic Local Density of States in Nanostructures with a Scanning Tunneling Microscope. ACS Photonics, 7(5), 1280–1289.
Résumé: A novel technique for the investigation of the radiative contribution to the electromagnetic local density of states is presented. The inelastic tunneling current from a scanning tunneling microscope (STM) is used to locally and electrically excite the plasmonic modes of a triangular gold platelet. The radiative decay of these modes is detected through the transparent substrate in the far field. Emission spectra, which depend on the position of the STM excitation, as well as energy-filtered emission maps for particular spectral windows are acquired using this technique. The STM-nanosource spectroscopy and microscopy results are compared to those obtained from spatially resolved electron energy loss spectroscopy (EELS) maps on similar platelets. While EELS is known to be related to the total projected electromagnetic local density of states, the light emission from the STM-nanosource is shown here to select the radiative contribution. Full electromagnetic calculations are carried out to explain the experimental STM data and provide valuable insight into the radiative nature of the different contributions of the breathing and edge plasmon modes of the nanoparticles. Our results introduce the STM-nanosource as a tool to investigate and engineer light emission at the nanoscale.
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Debiossac, M., Roncin, P., & Borisov, A. G. (2020). Refraction of Fast Ne Atoms in the Attractive Well of a LiF(001) Surface. J. Phys. Chem. Lett., 11, 4564–4569.
Résumé: Ne atoms with energies of </=3 keV are diffracted under grazing angles of incidence from a LiF(001) surface. For a small momentum component of the incident beam perpendicular to the surface, we observe an increase in the elastic rainbow angle together with a broadening of the inelastic scattering profile. We interpret these two effects as the refraction of the atomic wave in the attractive part of the surface potential. We use a fast, rigorous dynamical diffraction calculation to find a projectile-surface potential model that enables a quantitative reproduction of the experimental data for </=10 diffraction orders. This allows us to extract an attractive potential well depth of 10.4 meV. Our results set a benchmark for more refined surface potential models that include the weak van der Waals region, a long-standing challenge in the study of atom-surface interactions.
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Ludwig, M., Aguirregabiria, G., Ritzkowsky, F., Rybka, T., Marinica, D. C., Aizpurua, J., Borisov, A. G., Leitenstorfer, A., & Brida D. (2020). Sub-femtosecond electron transport in a nanoscale gap. Nat. Phys., 16, 341–345.
Résumé: The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion.
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Ludwig, M., Kazansky, A. K., Aguirregabiria, G., Marinica, D. C., Falk, M., Leitenstorfer, A., Brida, D., Aizpurua, J., & Borisov, A. G. (2020). Active control of ultrafast electron dynamics in plasmonic gaps using an applied bias. Phys. Rev. B, 101(24), 241412.
Résumé: In this joint experimental and theoretical study we demonstrate coherent control of the optical field emission and electron transport in plasmonic gaps subjected to intense single-cycle laser pulses. Our results show that an external THz field or a minor dc bias, orders of magnitude smaller than the optical bias owing to the laser field, allows one to modulate and direct the electron photocurrents in the gap of a connected nanoantenna operating as an ultrafast nanoscale vacuum diode for lightwave electronics. Using time-dependent density functional theory calculations we elucidate the main physical mechanisms behind the observed effects and show that an applied dc field significantly modifies the optical field emission and quiver motion of photoemitted electrons within the gap. The quantum many-body theory reproduces the measured net electron transport in the experimental device, which allows us to establish a paradigm for controlling nanocircuits at petahertz frequencies.
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2019 |
Aguilar-Galindo, F., Diaz-Tendero, S., & Borisov, A. G. (2019). Electronic Structure Effects in the Coupling of a Single Molecule with a Plasmonic Antenna. J. Phys. Chem. C, 123(7), 4446–4456.
Résumé: Miniaturization of plasmonic devices and the possibility to address single-molecule quantum emitters (QEs) in plasmonic cavities allow one to approach a regime where the characteristic sizes of the system are on the scale of molecular dimensions. In such a situation, the actual spatial profile of the transition electron density associated with a molecular exciton affects the coupling between molecular excitons and metal (nano)objects. Using a quantum approach, we address the energies and lifetimes of the excited states of the zinc phthalocyanine dye molecule placed in the nanometer vicinity of a plasmonic antenna. We demonstrate that the interaction between the molecular excitons and a metal nanoparticle reflects the gross features of the atomic structure in the molecule. The possibility to “look” inside the molecule does not require the presence of atomic scale probes on the surfaces of plasmonic nanoparticles, which would lead to the corresponding localization of the optical field. We show that the QE itself simultaneously generates highly localized fields and probes them via self-interaction.
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Aguirregabiria, G., Marinica, D. C., Ludwig, M., Brida, D., Leitenstorfer, A., Aizpurua, J., & Borisov, A. G. (2019). Dynamics of electron-emission currents in plasmonic gaps induced by strong fields. Faraday Discus., 214, 147–157.
Résumé: The dynamics of ultrafast electron currents triggered by femtosecond laser pulse irradiation of narrow gaps in a plasmonic dimer is studied using quantum mechanical Time-Dependent Density Functional Theory (TDDFT). The electrons are injected into the gap due to the optical field emission from the surfaces of the metal nanoparticles across the junction. Further evolution of the electron currents in the gap is governed by the locally enhanced electric fields. The combination of TDDFT and classical modelling of the electron trajectories allows us to study the quiver motion of the electrons in the gap region as a function of the Carrier Envelope Phase (CEP) of the incident pulse. In particular, we demonstrate the role of the quiver motion in establishing the CEP-sensitive net electric transport between nanoparticles.
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Riemensberger, J., Neppl, S., Potamianos, D., Schaffer, M., Schnitzenbaumer, M., Ossiander, M., Schroder, C., Guggenmos, A., Kleineberg, U., Menzel, D., Allegretti, F., Barth, J. V., Kienberger, R., Feulner, P., Borisov, A. G., Echenique, P. M., & Kazansky A. K. (2019). Attosecond Dynamics of sp-Band Photoexcitation. Phys. Rev. Lett., 123(17), 176801.
Résumé: We report measurements of the temporal dynamics of the valence band photoemission from the magnesium (0001) surface across the resonance of the ¯Γ surface state at 134 eV and link them to observations of high-resolution synchrotron photoemission and numerical calculations of the time-dependent Schrödinger equation using an effective single-electron model potential. We observe a decrease in the time delay between photoemission from delocalized valence states and the localized core orbitals on resonance. Our approach to rigorously link excitation energy-resolved conventional steady-state photoemission with attosecond streaking spectroscopy reveals the connection between energy-space properties of bound electronic states and the temporal dynamics of the fundamental electronic excitations underlying the photoelectric effect.
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2018 |
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Aguirregabiria, G., Marinica, D. C., Esteban, R., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2018). Role of electron tunneling in the nonlinear response of plasmonic nanogaps. Phys. Rev. B, 97(11), 115430.
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Marinica, D. C., Silkin, V. M., Kazansky, A. K., & Borisov, A. G. (2018). Controlling gap plasmons with quantum resonances. Phys. Rev. B, 98(15), 155426.
Résumé: We use classical electrodynamics, time-dependent density functional theory, and random-phase approximation to study the gap plasmons propagating in the nm-wide gap between metal surfaces. Particular emphasis is given to the quantum effects emerging when the junction is functionalized with a nanostructure supporting unoccupied gap localized electronic states. With the example of a quantum well (QW) introduced in the junction we show that the optically assisted electron transport across the junction via the gateway QW localized electronic states might strongly affect the lifetime and the propagation length of the gap plasmon. The coupling to the single-particle electron-hole excitations from occupied electronic states at metal surfaces into the QW-localized electronic states provides an efficient decay channel of the gap plasmon mode. Different from the through-gap electron tunneling discussed in the plasmonics literature, the electron transport involving the gateway electronic state is characterized by the threshold behavior with plasmon frequency. As a consequence, the dynamics of the gap plasmon can be controlled by varying the binding energy of the QW-localized electronic state. In more general terms, our results demonstrate strong sensitivity of the gap plasmons to the optically assisted electron transport properties of the junction which opens further perspectives in design of nanosensors and integrated active optical devices.
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2017 |
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Aguirregabiria, G., Marinica, D. C., Esteban, R., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2017). Electric Field-Induced High Order Nonlinearity in Plasmonic Nanoparticles Retrieved with Time-Dependent Density Functional Theory. ACS Photonics, 4(3), 613–620.
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Debiossac, M., Atkinson, P., Zugarramurdi, A., Eddrief, M., Finocchi, F., Etgens, V. H., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2017). Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination. Appl. Surf. Sci., 391, 53–58.
Résumé: brief oveview of the benefit of having a grazing incidence fast atom diffraction (GIFAD) setup inside a molecular beam eppitaxy setup.
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Herrera, M. Z., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2017). Quantum description of the optical response of charged monolayer–thick metallic patch nanoantennas. Phys. Rev. B, 95(24), 245413.
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Koval, N. E., Borisov, A. G., Rosa, L. F. S., Stori, E. M., Dias, J. F., Grande, P. L., Sánchez-Portal, D., & Muiño, R. D. (2017). Vicinage effect in the energy loss of H2 dimers: Experiment and calculations based on time-dependent density-functional theory. Phys. Rev. A, 95(6), 062707.
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Marinica, D. C., Kazansky, A. K., & Borisov, A. G. (2017). Electrical control of the light absorption in quantum-well functionalized junctions between thin metallic films. Phys. Rev. B, 96(24), 245407.
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Matias da Silva, F., Fadanelli Filho, R. C., Grande, P. L., Koval, N., Diez Muino, R., Borisov, A. G., Arista, N., & Schiwietz G. (2017). Ground-and excited-state scattering potentials for the stopping of protons in an electron gas. J. Phys. B: At. Mol. Opt. Phys., 50(18), 185201.
Résumé: The self-consistent electron–ion potential V(r) is calculated for H+ ions in an electron gas system as a function of the projectile energy to model the electronic stopping power for conduction-band electrons. The results show different self-consistent potentials at low projectile-energies, related to different degrees of excitation of the electron cloud surrounding the intruder ion. This behavior can explain the abrupt change of velocity dependent screening-length of the potential found by the use of the extended Friedel sum rule and the possible breakdown of the standard free electron gas model for the electronic stopping at low projectile energies. A dynamical interpolation of V(r) is proposed and used to calculate the stopping power for H+ interacting with the valence electrons of Al. The results are in good agreement with the TDDFT benchmark calculations as well as with experimental data.
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Matias, F., Fadanelli, R. C., Grande, P. L., Koval, N. E., Muiño, R. D., Borisov, A. G., Arista, N. R., & Schiwietz, G. (2017). Ground- and excited-state scattering potentials for the stopping of protons in an electron gas. J. Phys. B: At. Mol. Opt. Phys., 50(18), 185201.
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2016 |
Gruber, E., Wilhelm, R. A., Petuya, R., Smejkal, V., Kozubek, R., Hierzenberger, A., Bayer, B. C., Aldazabal, I., Kazansky, A. K., Libisch, F., Krasheninnikov, A. V., Schleberger, M., Facsko, S., Borisov, A. G., Arnau, A., & Aumayr, F. (2016). Ultrafast electronic response of graphene to a strong and localized electric field. Nat. Commun., 7, 13948.
Résumé: The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 10(12) A cm(-2), the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics.
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Le Moal, E., Marguet, S., Canneson, D., Rogez, B., Boer-Duchemin, E., Dujardin, G., Teperik, T. V., Marinica, D. C., & Borisov, A. G. (2016). Engineering the emission of light from a scanning tunneling microscope using the plasmonic modes of a nanoparticle. Phys. Rev. B, 93(3), 035418.
Résumé: The inelastic tunnel current in the junction formed between the tip of a scanning tunneling microscope (STM) and the sample can electrically generate optical signals. This phenomenon is potentially of great importance for nano-optoelectronic devices. In practice, however, the properties of the emitted light are difficult to control because of the strong influence of the STM tip. In this work, we show both theoretically and experimentally that the sought-after, well-controlled emission of light from an STM tunnel junction may be achieved using a nonplasmonic STM tip and a plasmonic nanoparticle on a transparent substrate. We demonstrate that the native plasmon modes of the nanoparticle may be used to engineer the light emitted in the substrate. Both the angular distribution and intensity of the emitted light may be varied in a predictable way by choosing the excitation position of the STM tip on the particle.
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Marinica, D. - C., Aizpurua, J., & Borisov, A. G. (2016). Quantum effects in the plasmon response of bimetallic core-shell nanostructures. Opt. Express, 24(21), 23941–23956.
Résumé: We report a quantum mechanical study of the plasmonic response of bimetallic spherical core/shell nanoparticles. The systems comprise up to 10<sup>4</sup> electrons and their optical response is addressed with Time Dependent Density Functional Theory calculations. These quantum results are compared with classical electromagnetic calculations for core/shell systems formed by Al/Na, Al/Au and Ag/Na, as representative examples of bimetallic systems. We show that for shell widths in the nanometer range, the system cannot be described as a simple stack of two metals. The finite size effect and the transition layer formed between the core and the shell strongly modify the optical properties of the compound nanoparticle. In particular this configuration leads to a frequency shift of the plasmon resonance with shell character and an increased plasmon decay into electron-hole pairs which eventually quenches this resonance for very thin shells. This effect is difficult to capture with a classical theory even upon adjustment of the parameters of a combination of metallic dielectric functions.
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Teperik, T. V., Kazansky, A. K., & Borisov, A. G. (2016). Electron tunneling through water layer in nanogaps probed by plasmon resonances. Phys. Rev. B, 93(15), 155431.
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Zapata Herrera, M., Aizpurua, J., Kazansky, A. K., & Borisov, A. G. (2016). Plasmon Response and Electron Dynamics in Charged Metallic Nanoparticles. Langmuir, 32(11), 2829–2840.
Résumé: Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment.
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Zhu, W., Esteban, R., Borisov, A. G., Baumberg, J. J., Nordlander, P., Lezec, H. J., Aizpurua, J., & Crozier, K. B. (2016). Quantum mechanical effects in plasmonic structures with subnanometre gaps. Nat. Commun., 7, 11495.
Résumé: Metallic structures with nanogap features have proven highly effective as building blocks for plasmonic systems, as they can provide a wide tuning range of operating frequencies and large near-field enhancements. Recent work has shown that quantum mechanical effects such as electron tunnelling and nonlocal screening become important as the gap distances approach the subnanometre length-scale. Such quantum effects challenge the classical picture of nanogap plasmons and have stimulated a number of theoretical and experimental studies. This review outlines the findings of many groups into quantum mechanical effects in nanogap plasmons, and discusses outstanding challenges and future directions.
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2015 |
Barbry, M., Koval, P., Marchesin, F., Esteban, R., Borisov, A. G., Aizpurua, J., & Sanchez-Portal, D. (2015). Atomistic near-field nanoplasmonics: reaching atomic-scale resolution in nanooptics. Nano Lett., 15(5), 3410–3419.
Résumé: Electromagnetic field localization in nanoantennas is one of the leitmotivs that drives the development of plasmonics. The near-fields in these plasmonic nanoantennas are commonly addressed theoretically within classical frameworks that neglect atomic-scale features. This approach is often appropriate since the irregularities produced at the atomic scale are typically hidden in far-field optical spectroscopies. However, a variety of physical and chemical processes rely on the fine distribution of the local fields at this ultraconfined scale. We use time-dependent density functional theory and perform atomistic quantum mechanical calculations of the optical response of plasmonic nanoparticles, and their dimers, characterized by the presence of crystallographic planes, facets, vertices, and steps. Using sodium clusters as an example, we show that the atomistic details of the nanoparticles morphologies determine the presence of subnanometric near-field hot spots that are further enhanced by the action of the underlying nanometric plasmonic fields. This situation is analogue to a self-similar nanoantenna cascade effect, scaled down to atomic dimensions, and it provides new insights into the limits of field enhancement and confinement, with important implications in the optical resolution of field-enhanced spectroscopies and microscopies.
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Esteban, R., Aguirregabiria, G., Borisov, A. G., Wang, Y. M., Nordlander, P., Bryant, G. W., & Aizpurua, J. (2015). The Morphology of Narrow Gaps Modifies the Plasmonic Response. ACS Photonics, 2(2), 295–305.
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Esteban, R., Zugarramurdi, A., Zhang, P., Nordlander, P., Garcia-Vidal, F. J., Borisov, A. G., & Aizpurua, J. (2015). A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations. Faraday Discuss., 178, 151–183.
Résumé: The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few Angstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation.
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Lin, L., Zapata, M., Xiong, M., Liu, Z., Wang, S., Xu, H., Borisov, A. G., Gu, H., Nordlander, P., Aizpurua, J., & Ye, J. (2015). Nanooptics of Plasmonic Nanomatryoshkas: Shrinking the Size of a Core-Shell Junction to Subnanometer. Nano Lett., 15(10), 6419–6428.
Résumé: Quantum effects in plasmonic systems play an important role in defining the optical response of structures with subnanometer gaps. Electron tunneling across the gaps can occur, altering both the far-field optical response and the near-field confinement and enhancement. In this study, we experimentally and theoretically investigate plasmon coupling in gold “nanomatryoshka” (NM) nanoparticles with different core-shell separations. Plasmon coupling effects between the core and the shell become significant when their separation decreases to 15 nm. When their separation decreases to below 1 nm, the near- and far-field properties can no longer be described by classical approaches but require the inclusion of quantum mechanical effects such as electron transport through the self-assembled monolayer of molecular junction. In addition, surface-enhanced Raman scattering measurements indicate strong electron-transport induced charge transfer across the molecular junction. Our quantum modeling provides an estimate for the AC conductances of molecules in the junction. The insights acquired from this work pave the way for the development of novel quantum plasmonic devices and substrates for surface-enhanced Raman scattering.
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Marinica, D. C., Zapata, M., Nordlander, P., Kazansky, A. K., M Echenique, P., Aizpurua, J., & Borisov, A. G. (2015). Active quantum plasmonics. Sci. Adv., 1(11), e1501095.
Résumé: The ability of localized surface plasmons to squeeze light and engineer nanoscale electromagnetic fields through electron-photon coupling at dimensions below the wavelength has turned plasmonics into a driving tool in a variety of technological applications, targeting novel and more efficient optoelectronic processes. In this context, the development of active control of plasmon excitations is a major fundamental and practical challenge. We propose a mechanism for fast and active control of the optical response of metallic nanostructures based on exploiting quantum effects in subnanometric plasmonic gaps. By applying an external dc bias across a narrow gap, a substantial change in the tunneling conductance across the junction can be induced at optical frequencies, which modifies the plasmonic resonances of the system in a reversible manner. We demonstrate the feasibility of the concept using time-dependent density functional theory calculations. Thus, along with two-dimensional structures, metal nanoparticle plasmonics can benefit from the reversibility, fast response time, and versatility of an active control strategy based on applied bias. The proposed electrical manipulation of light using quantum plasmonics establishes a new platform for many practical applications in optoelectronics.
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Zapata, M., Camacho Beltran, A. S., Borisov, A. G., & Aizpurua, J. (2015). Quantum effects in the optical response of extended plasmonic gaps: validation of the quantum corrected model in core-shell nanomatryushkas. Opt. Express, 23(6), 8134–8149.
Résumé: Electron tunneling through narrow gaps between metal nanoparticles can strongly affect the plasmonic response of the hybrid nanostructure. Although quantum mechanical in nature, this effect can be properly taken into account within a classical framework of Maxwell equations using the so-called Quantum Corrected Model (QCM). We extend previous studies on spherical cluster and cylindrical nanowire dimers where the tunneling current occurs in the extremely localized gap regions, and perform quantum mechanical time dependent density functional theory (TDDFT) calculations of the plasmonic response of cylindrical core-shell nanoparticles (nanomatryushkas). In this axially symmetric situation, the tunneling region extends over the entire gap between the metal core and the metallic shell. For core-shell separations below 0.5 nm, the standard classical calculations fail to describe the plasmonic response of the cylindrical nanomatryushka, while the QCM can reproduce the quantum results. Using the QCM we also retrieve the quantum results for the absorption cross section of the spherical nanomatryushka calculated by V. Kulkarni et al. [Nano Lett. 13, 5873 (2013)]. The comparison between the model and the full quantum calculations establishes the applicability of the QCM for a wider range of geometries that hold tunneling gaps.
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2014 |
Debiossac, M., Zugarramurdi, A., Lunca-Popa, P., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2014). Transient Quantum Trapping of Fast Atoms at Surfaces. Phys. Rev. Lett., 112(2).
Résumé: We report on the experimental observation and theoretical study of the bound state resonances in fast atom diffraction at surfaces. In our studies, the He-4 atom beam has been scattered from a high-quality LiF(001) surface at very small grazing incidence angles. In this regime, the reciprocal lattice vector exchange with the surface allows transient trapping of the 0.3-0.5 keV projectiles into the quasistationary states bound by the attractive atom-surface potential well which is only 10 meV deep. Analysis of the linewidths of the calculated and measured resonances reveals that prior to their release, the trapped projectiles preserve their coherence over travel distances along the surface as large as 0.2 μm, while being in average only at some angstroms in front of the last atomic plane.
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Debiossac, M. and Z., A. and Khemliche, H. and Roncin, P. and Borisov, A. G. and Momeni, A. and Atkinson, P. and Eddrief, M. and Finocchi, F. and Etgens, V. H. (2014). Combined experimental and theoretical study of fast atom diffraction on the β2(2×4) reconstructed GaAs(001) surface. Phys. Rev. B, 90(15), 155308.
Résumé: A grazing incidence fast atom diffraction (GIFAD or FAD) setup, installed on a molecular beam epitaxy chamber, has been used to characterize the β2(2×4) reconstruction of a GaAs(001) surface at 530∘C under an As4 overpressure. Using a 400-eV 4He beam, high-resolution diffraction patterns with up to eighty well-resolved diffraction orders are observed simultaneously, providing a detailed fingerprint of the surface structure. Experimental diffraction data are in good agreement with results from quantum scattering calculations based on an ab initio projectile-surface interaction potential. Along with exact calculations, we show that a straightforward semiclassical analysis allows the features of the diffraction chart to be linked to the main characteristics of the surface reconstruction topography. Our results demonstrate that GIFAD is a technique suitable for measuring in situ the subtle details of complex surface reconstructions. We have performed measurements at very small incidence angles, where the kinetic energy of the projectile motion perpendicular to the surface can be reduced to less than 1 meV. This allowed the depth of the attractive van der Waals potential well to be estimated as −8.7 meV in very good agreement with results reported in literature.
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2013 |
Borisov, A. G., Sanchez-Portal, D., Kazansky, A. K., & Echenique, P. M. (2013). Resonant and nonresonant processes in attosecond streaking from metals. Phys. Rev. B, 87(12), 121110.
Résumé: We report on the theoretical study of laser-assisted attosecond photoemission from metals. The full time-dependent quantum approach reveals the role of the resonant interband and nonresonant surface emission processes in formation of final atto-streaking spectra. The present results explain recent experimental data on magnesium and show that the valence band streaking essentially reflects the respective weight of surface and resonant bulk electron ejection. DOI: 10.1103/PhysRevB.87.121110
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Koval, N. E., Sánchez-Portal, D., Borisov, A. G., & Díez Muiño, R. (2013). Dynamic screening and energy loss of antiprotons colliding with excited Al clusters. Nucl. Instrum. Methods Phys. Res., B, 317, 56–60.
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Marinica, D. C., Lourenco-Martins, H., Aizpurua, J., & Borisov, A. G. (2013). Plexciton quenching by resonant electron transfer from quantum emitter to metallic nanoantenna. Nano Lett., 13(12), 5972–5978.
Résumé: Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes short-lived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surface-enhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others.
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Teperik, T. V., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2013). Quantum effects and nonlocality in strongly coupled plasmonic nanowire dimers. Opt. Express, 21(22), 27306.
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Zugarramurdi, A., & Borisov, A. G. (2013). When fast atom diffraction turns 3D. Nucl. Instrum. Methods Phys. Res., B, 317, 83–89.
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2012 |
Borisov, A. G., Echenique, P. M., & Kazansky, A. K. (2012). Attostreaking with metallic nano-objects. New J. Phys., 14, 023036.
Résumé: The application of atto-second streaking spectroscopy (ASS) to direct time-domain studies of the plasmonic excitations in metallic nano-objects is addressed theoretically. The streaking spectrograms for a rectangular gold nano-antenna and spherical gold clusters are obtained within strong field approximation using classical electron trajectory calculations. The results reported here for spherical clusters are also representative of spherical nano-shells. This study demonstrates that ASS allows for detailed characterization of plasmonic modes, including near-field enhancement, frequency and decay rate. The role of the inhomogeneity of the induced electric fields is also demonstrated.
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Esteban, R., Borisov, A. G., Nordlander, P., & Aizpurua, J. (2012). Bridging quantum and classical plasmonics with a quantum-corrected model. Nat. Commun., 3, 825.
Résumé: Electromagnetic coupling between plasmonic resonances in metallic nanoparticles allows for engineering of the optical response and generation of strong localized near-fields. Classical electrodynamics fails to describe this coupling across sub-nanometer gaps, where quantum effects become important owing to non-local screening and the spill-out of electrons. However, full quantum simulations are not presently feasible for realistically sized systems. Here we present a novel approach, the quantum-corrected model (QCM), that incorporates quantum-mechanical effects within a classical electrodynamic framework. The QCM approach models the junction between adjacent nanoparticles by means of a local dielectric response that includes electron tunnelling and tunnelling resistivity at the gap and can be integrated within a classical electrodynamical description of large and complex structures. The QCM predicts optical properties in excellent agreement with fully quantum mechanical calculations for small interacting systems, opening a new venue for addressing quantum effects in realistic plasmonic systems.
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Marinica, D. C., Kazansky, A. K., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2012). Quantum Plasmonics: Nonlinear Effects in the Field Enhancement of a Plasmonic Nanoparticle Dimer. Nano Lett., 12(3), 1333–1339.
Résumé: A fully quantum mechanical investigation using time-dependent density functional theory reveals that the field enhancement in a coupled nanoparticle dimer can be strongly affected by nonlinear effects. We show that both classical as well as linear quantum mechanical descriptions of the system fail even for moderate incident light intensities. An interparticle current resulting from the strong field photo emission tends to neutralize the plasmon-induced surface charge densities on the opposite sides of the nanoparticle junction. Thus, the coupling between the two nanoparticles and the field enhancement is reduced as compared to linear theory. A substantial nonlinear effect is revealed already at incident powers of 10(9) W/cm(2) for interparticle separation distances as large as 1 nm and down to the touching limit.
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Savage, K. J., Hawkeye, M. M., Esteban, R., Borisov, A. G., Aizpurua, J., & Baumberg, J. J. (2012). Revealing the quantum regime in tunnelling plasmonics. Nature, 491(7425), 574–577.
Résumé: When two metal nanostructures are placed nanometres apart, their optically driven free electrons couple electrically across the gap. The resulting plasmons have enhanced optical fields of a specific colour tightly confined inside the gap. Many emerging nanophotonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for high-sensitivity chemical and biological sensors(1), nanoscale control of active devices(2-4), and improved photovoltaic devices(5). But for subnanometre gaps, coherent quantum tunnelling becomes possible and the system enters a regime of extreme non-locality in which previous classical treatments(6-14) fail. Electron correlations across the gap that are driven by quantum tunnelling require a new description of non-local transport, which is crucial in nanoscale optoelectronics and single-molecule electronics. Here, by simultaneously measuring both the electrical and optical properties of two gold nanostructures with controllable subnanometre separation, we reveal the quantum regime of tunnelling plasmonics in unprecedented detail. All observed phenomena are in good agreement with recent quantum-based models of plasmonic systems(15), which eliminate the singularities predicted by classical theories. These findings imply that tunnelling establishes a quantum limit for plasmonic field confinement of about 10(-8) lambda(3) for visible light (of wavelength lambda). Our work thus prompts new theoretical and experimental investigations into quantum-domain plasmonic systems, and will affect the future of nanoplasmonic device engineering and nanoscale photochemistry.
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Schubert, K., Damm, A., Eremeev, S. V., Marks, M., Shibuta, M., Berthold, W., Guedde, J., Borisov, A. G., Tsirkin, S. S., Chulkov, E. V., & Hoefer, U. (2012). Momentum-resolved electron dynamics of image-potential states on Cu and Ag surfaces. Phys. Rev. B, 85(20), 205431.
Résumé: The dependence of the inelastic lifetime of electrons in the first n = 1 image-potential state of clean and rare-gas covered Ag(111), Cu(111), and Cu(100) surfaces on their momentum parallel to the surface has been studied experimentally by means of time-and angle-resolved two-photon photoemission spectroscopy (2PPE) and theoretically by calculations based on the many-body theory within the self-energy formalism. Similar to the previously studied clean Cu(100) surface, the theoretical results are in excellent agreement with the experiment findings for Cu(111). For Ag(111), the theory overestimates the decay rate and its momentum dependence, which is attributed to the neglect of surface plasmon excitations. With increasing parallel momentum, the n = 1 state shifts out of the projected bulk band gap on both surfaces and turns into an image-potential resonance. This opens an additional decay channel by resonant electron transfer into the bulk, which is theoretically treated by the application of the wave packet propagation approach. The expected stronger increase of the decay rate upon crossing the edge of the band gap, however, is not observed in the experiment. The decoupling of the image-potential states from the metal surface upon adsorption of rare-gas layers results in a decrease of the decay rate as well as of its momentum dependence by a similar factor, which can be successfully explained by the change of interband and intraband contributions to the total decay rate.
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Zugarramurdi, A., Zabala, N., Silkin, V. M., Chulkov, E. V., & Borisov, A. G. (2012). Quantum-well states with image state character for Pb overlayers on Cu(111). Phys. Rev. B, 86(7), 075434.
Résumé: We study theoretically the quantum well states (QWSs) localized in Pb overlayers on Cu(111) surface. Particular emphasis is given to the states with energies close to the vacuum level. Inclusion of the long-range image potential tail into the model potential description of the system allows us to show the effect of hybridization between QWSs and image potential states (ISs). The particle-in-a-box energy sequence characteristic for QWSs evolves into the Rydberg series converging towards the vacuum level. The electron density of the corresponding states is partially moved from inside the metal overlayer into the vacuum. The decay rates due to the inelastic electron-electron scattering decrease with increasing energy, opposite to “conventional” QWSs and similar to the ISs. Many-body and wave packet propagation calculations of the inelastic decay rates are supplemented by simple analysis based on the phase accumulation model and wave-function penetration approximation. This allows an analytical description of the dependence of the QWS/ISs hybridization on different parameters and, in particular, on the overlayer thickness.
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2011 |
Stepanow, S., Mugarza, A., Ceballos, G., Gambardella, P., Aldazabal, I., Borisov, A. G., & Arnau, A. (2011). Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100). Phys. Rev. B, 83(11), 115101.
Résumé: We report on a joint scanning tunneling microscopy (STM) and theoretical wave packet propagation study of field emission resonances (FER's) of nanosized alkali metal clusters deposited on a Cu(100) surface. In addition to FER's of the pristine Cu(100) surface, we observe the appearance of island-induced resonances that are particularly well resolved for STM bias voltage values corresponding to electron energies inside the projected band gap of the substrate. The corresponding dI/dV maps reveal island-induced resonances of different nature. Their electronic densities are localized either inside the alkali cluster or on its boundaries. Our model calculations allow us to explain the experimental results as due to the coexistence and mixing of two kinds of island-induced states. On the one side, since the alkali work function is lower than that of the substrate, the nanosized alkali metal clusters introduce intrinsic localized electronic states pinned to the vacuum level above the cluster. These states can be seen as the FER's of the complete alkali overlayer quantized by the cluster boundaries. On the other side, the attractive potential well due to the alkali metal cluster leads to two-dimensional (2D) localization of the FER's of the Cu(100) surface, the corresponding split component of the resonances appearing below the bottom of the parent continuum. Our main conclusions are based on the attractive nature of the alkali ad-island potential. They are of general validity and, therefore, significant to understand electron confinement in 2D.
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Zugarramurdi, A., Borisov, A. G., Zabala, N., Chulkov, E. V., & Puska, M. J. (2011). Clustering and conductance in breakage of sodium nanowires. Phys. Rev. B, 83(3), 035402.
Résumé: We study the conductance during the elongation and breakage of Na nanowires described with the ultimate jellium model. A combined approach is used where the nanowire breakage is simulated self-consistently within the density-functional theory, and the wave packet propagation technique is applied for ballistic electron transport. For certain conditions the breakage of the nanowire is preceded by formation of clusters of magic size in the break junction. This affects the conductance G, in particular the shape of the G = 3G(0) to G = G(0) (=2e(2)/h) step upon elongation. The observed trends can be explained as due to the transient trapping of ballistic electrons inside the cluster, leading to a resonant character of the electron transport through the break junction. The cluster-derived resonances appear as peak structures in the differential conductance which may serve as an experimental signature of clustering.
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Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Comment on “Phase Contribution of Image Potential on Empty Quantum Well States in Pb Islands on the Cu(111) Surface”. Phys. Rev. Lett., 106(24), 249601.
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Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Theoretical study of constant current scanning tunneling spectroscopy in Pb overlayers. Phys. Rev. B, 84(11), 115422.
Résumé: We present a theoretical study of the constant current scanning tunneling spectroscopy of quantum well states localized in Pb(111) overlayers on Cu(111) surfaces. The distance-voltage characteristic of the tunneling junction is obtained with a mixed approach. The wave packet propagation technique is applied to describe electron tunneling from the tip into the sample, and the density functional calculations provide the necessary inputs for the one-dimensional model potential representation of the system. The excited-state population decay mechanisms via inelastic electron-electron and electron-phonon interactions are taken into account with a bias-dependent absorbing potential introduced in the metal. Our results are in good agreement with recent experimental studies [Phys. Rev. Lett. 102, 196102 (2009), Phys. Rev. B 81, 205438 (2010)] over the energy range where the free-electron description of the Pb overlayer used here applies. We find that at high bias the quantum well states experience a Stark energy shift and partially acquire a character of field emission resonances. The present model study also sheds light at the experimentally observed departure of the energies of the quantum well states from the particle-in-a-box prediction for the bias above 4 eV. The measured trend can be consistently explained as due to the departure of the realistic Pb band structure in the Gamma-L direction from free-electron parabola when the electron momentum approaches the Gamma point.
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2010 |
Perez-Gonzalez, O., Zabala, N., Borisov, A. G., Halas, N. J., Nordlander, P., & Aizpurua, J. (2010). Optical Spectroscopy of Conductive Junctions in Plasmonic Cavities. Nano Lett., 10(8), 3090–3095.
Résumé: The optical properties of a nanoparticle dimer bridged by a conductive junction depend strongly on the junction conductivity. As the conductivity increases, the bonding dimer plasmon blueshifts and broadens. For large conductance, a low energy charge transfer plasmon also appears in the spectra with a line width that decreases with increasing conductance. A simple physical model for the understanding of the spectral feature is presented. Our finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.
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Quijada, M., Diez Muino, R., Borisov, A. G., Alonso, J. A., & Echenique, P. M. (2010). Lifetime of electronic excitations in metal nanoparticles. New J. Phys., 12, 053023.
Résumé: Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a one-electron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The well-known quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finite-size systems.
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Riedel, D., Delattre, R., Borisov, A. G., & Teperik, T. V. (2010). A Scanning Tunneling Microscope as a Tunable Nanoantenna for Atomic Scale Control of Optical-Field Enhancement. Nano Lett., 10(10), 3857–3862.
Résumé: The high stability of a low temperature (9 K) scanning tunneling microscope junction is used to precisely adjust the enhancement of an external pulsed vacuum ultraviolet (VUV) laser The ensuing VUV optical-field strength is mapped on an hydrogenated Si(100) surface by imprinting locally one-photon atomic scale hydrogen desorption Subsequent to irradiation, topography of the Si(100) H surface at the reacted area revealed a desorption spot with unprecedented atomic precision Our results show that the shapes. positions. and sizes of the desorption spots are correlated to the calculated optical-field structure, offering real control of the optical-held distribution at molecular scale
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2009 |
Teperik, T. V., & Borisov, A. G. (2009). Optical resonances in the scattering of light from a nanostructured metal surface: A three-dimensional numerical study. Phys. Rev. B, 79(24), 245409.
Résumé: We present the full three-dimensional numerical study of the scattering of light by the gold substrate composed of square periodic array of inverted pyramidal pits. The time-dependent wave-packet-propagation approach was used to extract the complete scattering matrix as well as the near fields. The role of the pit-localized and surface-supported plasmonic modes in resonant reflection spectra and field enhancement is revealed. We show that the resonances in the specular reflection arise because of the excitation of the pit-localized plasmons while resonant absorption is linked with excitation of the surface-plasmon polaritons. For certain structure parameters absorption can reach 100%. Our theoretical results are in a good agreement with recently published experimental data [N. M. B. Perney , Opt. Express 14, 847 (2006); Phys. Rev. B 76, 035426 (2007)]. We also show that present structure allows one to obtain zero specular reflection where all scattered intensity is redirected into the grazing beams.</p>.
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Zugarramurdi, A., Zabala, N., Silkin, V. M., Borisov, A. G., & Chulkov, E. V. (2009). Lifetimes of quantum well states and resonances in Pb overlayers on Cu(111). Phys. Rev. B, 80(11), 115425.
Résumé: We present results of calculations of the lifetimes of excited electrons (holes) in quantum well states and quantum well resonances in Pb overlayers supported on Cu(111). Many-body decay via inelastic energy relaxation and one-electron decay via energy-conserving one-electron transfer into the substrate are considered. One-electron energies and wave functions have been computed for different coverages of the Pb overlayer (from 1 to 18 monolayers) by using a one-dimensional pseudopotential for the entire overlayer-substrate system in the framework of density functional theory within the local density approximation. The elastic (energy-conserving resonant electron transfer) contribution to the total lifetime broadening of quantum well resonances has been calculated within the wave packet propagation method. The inelastic electron-electron (many-body) contribution to the lifetime broadening of both occupied and unoccupied quantum well states has been evaluated using GW approximation. The decay mechanisms of both quantum well states and quantum well resonances in thick overlayers are discussed.
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2008 |
Marinica, D. C., Borisov, A. G., & Shabanov, S. V. (2008). Bound States in the continuum in photonics. Phys. Rev. Lett., 100(18), 183902.
Résumé: With examples of two parallel dielectric gratings and two arrays of thin parallel dielectric cylinders, it is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width. Such resonances are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner. Potential applications of such photonic systems include: large amplification of electromagnetic fields within photonic structures and, hence, enhancement of nonlinear phenomena, biosensing, as well as perfect filters and waveguides for a particular frequency, and impurity detection.
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Quijada, M., Borisov, A. G., & Muino, R. D. (2008). Time-dependent density functional calculation of the energy loss of antiprotons colliding with metallic nanoshells. Phys. Status Solidi, 205(6), 1312–1316.
Résumé: Time-dependent density functional theory is used to study the interaction between antiprotons and metallic nanoshells. The ground state electronic proper-ties of the nanoshell are obtained in the jellium approximation. The energy lost by the antiproton during the collision is calculated and compared to that suffered by antiprotons traveling in metal clusters. The resulting energy loss per unit path length of material in thin nanoshells is larger than the corresponding quantity for clusters. It is shown that the collision process can be interpreted as the antiproton crossing of two nearly bi-dimensional independent metallic systems. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Teperik, T. V., Garcia de Abajo, F. J., Borisov, A. G., Abdelsalam, M., Bartlett, P. N., Sugawara, Y., & Baumberg, J. J. (2008). Omnidirectional absorption in nanostructured metal surfaces. Nature Photon., 2(5), 299–301.
Résumé: Light absorbers available at present provide far from optimal black-body performance. The need for more efficient absorbers is particularly acute on the microscale, where they can play a significant role in preventing crosstalk between optical interconnects, and also as thermal light-emitting sources. Several efforts have been made in this context to achieve near-total but directionally dependent absorption using periodic grating structures(1-7). However, the ability to absorb light completely for any incident direction of light remains a challenge. Here we show that total omnidirectional absorption of light can be achieved in nanostructured metal surfaces that sustain localized optical excitations. The effect is realized over a full range of incident angles and can be tuned throughout the visible and near-infrared regimes by scaling the nanostructure dimensions. We suggest that surfaces displaying omnidirectional absorption will play a key role in devising efficient photovoltaic cells in which the absorbed light leads to electron-hole pair production.
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2003 |
Borisov, A. G., Sidis, V., Roncin, P., Momeni, A., Khemliche, H., Mertens, A., & Winter, H. (2003). F- formation via simultaneous two-electron capture during grazing scattering of F+ ions from a LiF(001) surface. PHYSICAL REVIEW B, 67(11), 115403.
Résumé: For slow F+ ions (v<0.05 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence, large fractions of negative F- ions have recently been observed in the reflected beam, while for neutral F-0 projectiles no negative F- ions are produced in the same velocity range [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)]. From detailed studies on projectile energy loss and charge fractions, the conclusion was drawn that the F- ions are formed from F+ via a simultaneous capture of two electrons from adjacent F- sites at the surface. We present a theoretical description of the double-electron-capture process leading to F- formation from F+ projectiles grazingly scattered from the LiF(001) surface. We use quantum chemistry calculations to determine the relevant Hamiltonian matrix and close-coupling solution of the time-dependent Schrodinger equation. The theoretical results are in good agreement with experimental observations.
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2002 |
Khemliche, H., Borisov, A. G., Momeni, A., & Roncin, P. (2002). Exciton and trion formation during neutralization of Ne+ at a LiF(001) surface. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 221–225.
Résumé: The grazing angle interaction of 2 keV Ne+ projectiles with a LiF(0 0 1) surface is studied with the combination, in coincidence, of projectile and electron time-of-flight spectroscopy. The measurements reveal that besides the standard Auger neutralization process that leads to electron ejection, there is another neutralization mechanism that does not result in electron emission. The latter process has been identified as the formation of an electron-bihole complex termed trion. We report here the detailed study of the scattering angle dependence of these two neutralization channels, with comparison with the process leading to population of surface excitons. (C) 2002 Published by Elsevier Science B.V.
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