Peer-reviewed Publications |
Bergeron, H., Curado, E. M. F., Gazeau, J. P., & Rodrigues, L. M. C. S. (2013). Symmetric generalized binomial distributions. Journal of Mathematical Physics, 54(12), 123301.
Résumé: In two recent articles, we have examined a generalization of the binomial distribution associated with a sequence of positive numbers, involving asymmetric expressions of probabilities that break the symmetry win-loss. We present in this article another generalization (always associated with a sequence of positive numbers) that preserves the symmetry win-loss. This approach is also based on generating functions and presents constraints of non-negativeness, similar to those encountered in our previous articles. (C) 2013 AIP Publishing LLC.
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Bergeron, H., Gazeau, J. P., & Youssef, A. (2013). Are the Weyl and coherent state descriptions physically equivalent? PHYSICS LETTERS A, 377(8), 598–605.
Résumé: We investigate the consistency of coherent state quantization in regard to physical observations in the non-relativistic (or Galilean) regime. We compare this particular type of quantization of the complex plane with the canonical (Weyl) quantization and examine whether they are or not equivalent in their predictions. As far as only usual dynamical observables (position, momentum, energy, ...) are concerned, the quantization through coherent states is proved to be a perfectly valid alternative. We successfully put to the test the validity of CS quantization in the case of data obtained from vibrational spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.
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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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Garcia-Gil, S., Teillet-Billy, D., Rougeau, N., & Sidis, V. (2013). H Atom Adsorption on a Silicate Surface: The (010) Surface of Forsterite. JOURNAL OF PHYSICAL CHEMISTRY C, 117(24), 12612–12621.
Résumé: We present a first-principles computational study of the interaction of an H
atom with the (010) surface of forsterite (Mg2SiO4). Periodic DFT-GGA calculations (PBE)are carried out using the SIESTA code with core pseudopotentials and TZP localized basis sets. Potential energy curves are determined for the approach of the H atom toward different sites of the surface: atop, near, or in between the O, Mg, and Si atoms. An outer adsorption well is found for all investigated sites; it is deepest (162 meV) at a so-called “displaced Mg−O bridge” position. The binding at this well is of the “weak chemisorption”/“strongphysisorption” type. An inner stronger chemisorption well (670 meV deep) exists exclusivelynear an O site but not strictly atop. Depending on the path, we find activation barriers (25−170 meV high) against chemisorption, the lowest of these occurs for the top O site.General trends of the computed interaction energies qualitatively agree with the QM/MM results of Goumans et al. [Mon. Not. R. Astron. Soc. 2009, 393, 1403], but adsorption bindingenergies and barrier heights differ significantly.
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Gauyacq, J. P., & Lorente, N. (2013). Magnetic reversal of a quantum nanoferromagnet. PRB, 87(19), 195402.
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Gauyacq, J. P., Yaro, S. M., Cartoixa, X., & Lorente, N. (2013). Correlation-Mediated Processes for Electron-Induced Switching between Neel States of Fe Antiferromagnetic Chains. Phys. Rev. Lett., 110(8), 087201.
Résumé: The controlled switching between two quasistable Neel states in adsorbed antiferromagnetic Fe chains has recently been achieved by Loth et al. [Science 335, 196 (2012)] using tunneling electrons from an STM tip. In order to rationalize their data, we evaluate the rate of tunneling electron-induced switching between the Neel states. Good agreement is found with the experiment, permitting us to identify three switching mechanisms: (i) low STM voltage direct electron-induced transitions, (ii) intermediate STM voltage switching via spin-wave-like excitation, and (iii) high STM voltage transitions mediated by domain-wall formation. Spin correlations in the antiferromagnetic chains are the switching driving force, leading to a marked chain-size dependence. DOI: 10.1103/PhysRevLett.110.087201
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Han, D., Nave, S., & Jackson, B. (2013). Dissociative chemisorption of methane on Pt(110)-(1x2): effects of lattice motion on reactions at step edges. J Phys Chem A, 117(36), 8651–8659.
Résumé: The dissociative chemisorption of methane on Pt(110)-(1x2) is examined, with a focus on how the reaction dynamics are modified by the motion of the lattice atoms. The barriers to dissociation are found to be lowest at the step edges. The relaxation of the lattice in the presence of the dissociating molecule is found to be far more complicated than on the smooth surfaces of Pt and Ni. The dissociative sticking probabilities are computed using a full-dimensional treatment based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. The potential energy surface and all parameters in our model are computed from first principles. The effects of lattice motion are strong, but not significantly larger than for dissociation on smoother surfaces. Vibrational excitation of the molecule can significantly enhance reactivity, though this effect varies from mode to mode. Agreement with recent experiments with regard to the variation of reactivity with translational energy and substrate temperature is good.
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Jackson, B., & Nave, S. (2013). The dissociative chemisorption of methane on Ni(111): The effects of molecular vibration and lattice motion. JOURNAL OF CHEMICAL PHYSICS, 138(17), 174705.
Résumé: We examine the dissociative chemisorption of methane on a Ni(111) surface, using a fully quantum approach based on the Reaction Path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. The potential energy surface and all parameters in our model are computed from first principles. Vibrational excitation of the molecule is shown to significantly enhance the reaction probability, and the efficacy for this is explained in terms of the vibrationally non-adiabatic couplings, vibrational mode softening, and mode symmetry. Agreement with experimental data for molecules initially in the ground and 1nu3 state is good, and including lattice anharmonicity further improves our results. The variation of the dissociation probability with substrate temperature is well reproduced by the model, and is shown to result primarily from changes in the dissociation barrier height with lattice motion. The enhancement of dissociative sticking with substrate temperature is particularly strong for processes that would otherwise have insufficient energy to surmount the barrier. Our model suggests that vibrationally excited molecules are likely to dominate the “laser off” dissociative sticking at high nozzle temperatures.
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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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Schaffert, J., Cottin, M. C., Sonntag, A., Bobisch, C. A., Moeller, R., Gauyacq, J. - P., & Lorente, N. (2013). Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111). Phys. Rev. B, 88(7), 075410.
Résumé: The rates of a hindered molecular rotation induced by tunneling electrons are evaluated using scattering theory within the sudden approximation. Our approach explains the excitation of copper phthalocyanine molecules (CuPc) on Cu(111) as revealed in a recent measurement of telegraph noise in a scanning tunneling microscopy experiment [Schaffert et al., Nat. Mater. 12, 223 (2013)]. A complete explanation of the experimental data is performed by computing the geometry of the adsorbed system, its electronic structure, and the energy transfer between tunneling electrons and the molecule's rotational degree of freedom. The results unambiguously show that tunneling electrons induce a frustrated rotation of the molecule. In addition, the theory determines the spatial distribution of the frustrated rotation excitation, confirming the striking dominance of two out of four molecular lobes in the observed excitation process. This lobe selectivity is attributed to the different hybridizations with the underlying substrate.
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Schaffert, J., Cottin, M. C., Sonntag, A., Karacuban, H., Bobisch, C. A., Lorente, N., Gauyacq, J. - P., & Möller, R. (2013). Imaging the dynamics of individually adsorbed molecules. Nat. Mater., 12(3), 223–227.
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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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Teperik, T. V., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2013). Robust Subnanometric Plasmon Ruler by Rescaling of the Nonlocal Optical Response. Phys. Rev. Lett., 110(26), 263901.
Résumé: We present the optical response of two interacting metallic nanowires calculated for separation distances down to angstrom range. State-of-the-art local and nonlocal approaches are compared with full quantum time-dependent density functional theory calculations that give an exact account of nonlocal and tunneling effects. We find that the quantum results are equivalent to those from classical approaches when the nanoparticle separation is defined as the separation between centroids of the screening charges. This establishes a universal plasmon ruler for subnanometric distances. Such a ruler not only impacts the basis of many applications of plasmonics, but also provides a robust rule for subnanometric metrology.
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Tsirkin, S. S., Borisov, A. G., & Chulkov, E. V. (2013). Green's function approach to the lifetimes of image potential resonances at metal surfaces. Phys. Rev. B, 88(3), 035449.
Résumé: We present a theoretical study of the image potential resonances (IPRs) at metal surfaces. We develop the Green's functions approach allowing us to calculate binding energies E-n and lifetimes tau(n) of IPRs with high quantum numbers n (up to 10 in this work). A systematic study is performed at the (Gamma) over bar point for the close-packed metal surfaces: Cu(111), Ag(111), Au(111), Al(001), Al(111), Be(0001), Mg(0001), Na(110), Li(110), and also at the (Y) over bar point on Cu(110). The calculated lifetimes of IPRs on close-packed surfaces demonstrate the scaling law tau(n) proportional to n(3). Our results are in agreement with available experimental data. We show that at the (Y) over bar point on Cu(110) each quantum number n corresponds to a pair of IPRs n(+) and n(-), where the energy difference En+ – En- is proportional to n(-3). The lifetimes tau(n+) and tau(n-) differ significantly, however, they both obey the scaling law tau(n +/-) proportional to n(3). Since the electrons trapped in the long-lived IPRs are strongly localized on the vacuum side, we argue that the inelastic electron-electron and electron-phonon scattering have a small contribution to the decay rate of these IPRs. The latter is dominated by the resonant electron transfer into the bulk.
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Zugarramurdi, A., & Borisov, A. G. (2013). Theoretical study of the effect of beam misalignment in fast-atom diffraction at surfaces. Phys. Rev. A, 87(6), 062902.
Résumé: Typical applications of the fast-atom diffraction technique exploit incidence along low-index directions to extract accurate structural information on surfaces from the diffraction pattern. The data interpretation in this case is well developed and simplified by the axial channeling conditions, where the three-dimensional projectile-surface interaction appears effectively averaged over the fast-motion direction. We study theoretically the diffraction of fast-atom beams that are significantly misaligned with respect to a low-index direction at the surface. With full quantum wave-packet calculations, we address He atom scattering from the LiF(001) surface within a wide range of azimuthal and polar incidence angles. In particular, we are interested in the transitions between low-index directions upon the azimuthal rotation of the beam, and in the question of the choice of an adequate axial channeling approximation. We make use of the energy criterion to analyze the diffraction patterns and to discuss how the momentum exchange projected on the beam direction affects the diffraction.
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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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Zugarramurdi, A., Debiossac, M., Lunca-Popa, P., Alarcon, L. S., Momeni, A., Khemliche, H., Roncin, P., & Borisov, A. G. (2013). Surface-grating deflection of fast atom beams. Phys. Rev. A, 88(1), 0129074.
Résumé: For energetic atomic beams grazingly incident at the surface along the low index directions, fast motion parallel to the surface and slow motion perpendicular to the surface lead to the quantum diffraction pattern in the scattered beam. In this experimental and theoretical joint study we show that when the incident beam is misaligned with respect to an axial channel, the characteristic deformation of the diffraction pattern reflects an overall deflection of the scattered beam from the specular direction. The deflection is maximum for the azimuthal misalignment angles close to the rainbow angle and we show how this effect can be explained with the detailed balance principle relating diffraction of misaligned and perfectly aligned beams. We also demonstrate that using the detailed balance principle the diffraction charts for the incident beams aligned along the axial channel can be reconstructed from the azimuthal incidence angle dependence of the data obtained with misaligned beams.
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