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Gauyacq J.P.,CNRS Orsay Institute for Molecular Science | Lorente N.,Catalan Institute of Nanoscience and Nanotechnology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Excitation of finite chains of magnetic atoms adsorbed on a surface by tunneling electrons from a scanning tunneling microscope tip is studied using a Heisenberg Hamiltonian description of the magnetic couplings along the chain and a strong coupling approach to inelastic tunneling. The excitation probability of the magnetic levels is very high and the excitation spectra in chains of different lengths are very similar. The excitations in finite chains can be considered as spin waves quantized in the finite object. The energy and momentum spectra of the spin waves excited in the idealized infinite chain by tunneling electrons are determined from the results on the finite chains. Both ferromagnetic and antiferromagnetic couplings are considered, leading to very different results. In particular, in the antiferromagnetic case, excitations linked to the entanglement of the chain ground state are evidenced. © 2011 American Physical Society.

Gauyacq J.-P.,CNRS Orsay Institute for Molecular Science | Lorente N.,Catalan Institute of Nanoscience and Nanotechnology | Novaes F.D.,Catalan Institute of Nanoscience and Nanotechnology
Progress in Surface Science | Year: 2012

The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These structures were revealed by STM experiments in IBM Almaden in the early 2000s for atomic adsorbates on CuN surfaces. The experiments consisted in the study of the changes in conductance caused by inelastic tunneling of electrons (IETS, inelastic electron tunneling spectroscopy). Manganese and Iron adatoms were shown to have different magnetic anisotropies induced by the substrate. More experiments by other groups followed up, showing that magnetic excitations could be detected in a variety of systems: e.g. complex organic molecules showed that their magnetic anisotropy was dependent on the molecular environment, piles of magnetic molecules showed that they interact via intermolecular exchange interaction, spin waves were excited on ferromagnetic surfaces and in Mn chains, and magnetic impurities have been analyzed on semiconductors. These experiments brought up some intriguing questions: the efficiency of magnetic excitations was very high, the excitations could or could not involve spin flip of the exciting electron and singular-like behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis; perturbation theories, sudden-approximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, many-body approaches were also used to decipher the interplay between inelastic processes and the Kondo effect. Spin torque transfer has been shown to be effective in changing spin orientations of an adsorbate in theoretical works, and soon after it was shown experimentally. More recently, the previously mentioned strong coupling approach was extended to treat the excitation of spin waves in atomic chains and the ubiquitous role of electron-hole pair creation in de-exciting spins on surfaces has been analyzed. This review article expounds these works, presenting the theoretical approach by the authors while trying to thoroughly review parallel theoretical and experimental works. © 2012 Elsevier Ltd. All rights reserved.

Carcabal P.,CNRS Orsay Institute for Molecular Science | Cocinero E.J.,University of the Basque Country | Simons J.P.,University of Oxford
Chemical Science | Year: 2013

The strength of the interaction between three monosaccharides (O-phenyl-β-d-gluco-, β-d-galacto- and α-d-mannopyranoside) and a single water molecule has been investigated experimentally in the gas phase by means of 2-colour UV-UV ionisation and dissociation threshold measurements. Their binding energies have also been calculated using dispersion corrected DFT methods and the resolution of identity approximation. The calculated and experimental relative binding energies are in good correspondence at all considered levels of theory, and the RI-B97D+disp/TZVPP level of theory in particular, provides very good agreement with a considerable reduction in computational time. Although these systems experience some conformational changes upon photo-ionisation, the experimental measurements lead to reliable estimates of the binding energies of the different conformers of the monosaccharide-water complexes and their relative values reflect their structural differences. This journal is © The Royal Society of Chemistry 2013.

Ideguchi T.,Max Planck Institute of Quantum Optics | Poisson A.,CNRS Orsay Institute for Molecular Science | Guelachvili G.,CNRS Orsay Institute for Molecular Science | Picque N.,Ludwig Maximilians University of Munich | Hansch T.W.,Ludwig Maximilians University of Munich
Nature communications | Year: 2014

The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences.

Schliesser A.,Ecole Polytechnique Federale de Lausanne | Schliesser A.,Max Planck Institute of Quantum Optics | Picque N.,Max Planck Institute of Quantum Optics | Picque N.,Ludwig Maximilians University of Munich | And 3 more authors.
Nature Photonics | Year: 2012

Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science. © 2012 Macmillan Publishers Limited. All rights reserved.

Khoury A.Z.,Federal University of Fluminense | Milman P.,CNRS Orsay Institute for Molecular Science | Milman P.,University Paris Diderot
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We propose a polarization to orbital angular momentum teleportation scheme using entangled photon pairs generated by spontaneous parametric down-conversion. By making a joint detection of the polarization and angular momentum parity of a single photon, we are able to detect all the Bell states and perform, in principle, perfect teleportation from a discrete to a continuous system using minimal resources. The proposed protocol implementation demands experimental resources that are currently available in quantum optics laboratories. © 2011 American Physical Society.

Raseeva G.,CNRS Orsay Institute for Molecular Science
European Physical Journal D | Year: 2012

A model calculating the laser fields at a flat structureless surface taking into account the surface photoelectric effect is presented. The photon is p or transverse magnetic linearly polarized, continuous and its wave length is long, i.e. λvac ≥ 12.4 nm. The sharp rise of the electron density at the interface generates an atomic scale spatial dependence of the laser field. In real space and in the temporal gauge, the vector potential A of the laser is obtained as a solution of the classical Ampère-Maxwell and the material equations. The susceptibility is a product of the electron density of the material system with the surface and of the bulk tensor and non-local isotropic (TNLI) polarizability. The electron density is obtained quantum mechanically by solving the Schrödinger equation. The bulk TNLI polarizability including dispersion is calculated from a Drude-Lindhard-Kliewer model. In one dimension perpendicular to the surface the components Ax(z,ω) and Az(z,ω) of the vector potential are solutions of the Ampère- Maxwell system of two coupled integro-differential equations. The model, called vector potential from the electron density-coupled integro-differential equations (VPED-CIDE), is used here to obtain the electron escape probability from the power density absorption, the reflectance, the electron density induced by the laser and Feibelman's parameters d|| and d. Some preliminary results on aluminium surfaces are given here and in a companion paper the photoelectron spectra are calculated with results in agreement with the experiment. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.

Raseeva G.,CNRS Orsay Institute for Molecular Science
European Physical Journal D | Year: 2012

Using the model derived in paper I [G. Raşeev, Eur. Phys. J. D 66, 167 (2012)], this work presents calculations of the photoelectron spectrum (PES) of low index aluminium surfaces in the 10-30 eV region. The laser is p or transverse magnetic linearly polarized incident on a flat structureless surface and its fields are modeled in I using the vector potential in the temporal gauge. This model uses a tensor and nonlocal isotropic (TNLI) susceptibility and solves the classical Ampère-Maxwell equation through the use of the vector potential from the electron density-coupled integro-differential equations (VPED-CIDE). The PE cross sections are the squares of the PE transition moments calculated using the VPED-CIDE vector potential function of the penetration coordinate. The PES is obtained in a one step model using either the Fermi golden rule or the Weisskopf-Wigner (WW) expressions. The WW cross section PES compares favorably with the experimental angle and energy resolved photoelectron yield (AERPY) spectrum of Levinson et al. [Phys. Rev. Lett. 43, 952 (1979)], Levinson and Plummer [Phys. Rev. B 24, 628 (1981)] for Al(001) and of Barman et al. [Phys. Rev. B 58, R4285 (1998)], Barman [Curr. Sci. 88, 54 (2005)] for Al(111) surfaces. As in the experiment, our theoretical AERPY displays the multipole surface plasmon resonance at 11.32/12.75 eV for Al(001)/Al(111), mainly due to the surface contribution |ψf |p . A|ψ| 2, the bulk plasmon minimum at 15 eV and the two single particle excitation resonances at about 16 and 22 eV. The nature of the plasmon resonances of the PES is analyzed using the reflectance, the electron density induced by the laser and Feibelman's parameter d all introduced in paper I. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.

Zehnacker A.,CNRS Orsay Institute for Molecular Science
International Reviews in Physical Chemistry | Year: 2014

This review focuses on chirality effects in spectroscopy and photophysics of chiral molecules or protonated ions, and their weakly bound complexes, isolated in the gas phase. Low-temperature studies in jet-cooled conditions allow disentangling the different interactions at play and shed light on the ancillary interactions responsible for chiral recognition, like OH...π or CH...π, which would be blurred at room temperature. The consequences of these interactions on chiral recognition in condensed phase are described, as well as the influence of higher energy conformers, which can be accessed in room-temperature experiments. The role of kinetic effects and solvation in jet-cooled experiments is discussed. Last, examples of dramatic chirality effects in photo-induced dissociation are given. © 2014 Taylor & Francis.

Guillemot L.,CNRS Orsay Institute for Molecular Science | Bobrov K.,CNRS Orsay Institute for Molecular Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a scanning tunneling microscope study on reactivity of chemisorbed oxygen on the Cu(110)-(2×1)-O surface. We have found that the Cu(110)-(2×1)-O surface is intrinsically unstable under thermal annealing in the 400-900 K range. In the 455-570 K range, the surface undergoes faceting. The orientational transition of the adsorbed oxygen phase displays wide [110] terraces, covered by (2×1)-O bands self-assembled into a superstructure, as well as bunches of oxygen-free narrow terraces. We found that the wide [110] terraces are intrinsically unstable against further restructuring at their edges. The restructuration is driven by reversible thermal dissociation of the (2×1)-O bands. The slightly uneven oxygen band density between terraces, consequently differing in reactivity with respect to Cu-O fragments, induces Cu atom transport between their edges. The interplay between thermal dissociation of the (2×1)-O bands and long-range elastic relaxation of the strained surface is suggested to be the origin of the observed inhomogeneous oxygen distribution. In the 570-810 K range the Cu atom transport reveals continuous growth of the oxygenated [110] terraces. We discuss in detail the mechanism of the Cu transport, which results in a rapid propagation of the oxygenated terraces as well as a strain development on the surface. © 2011 American Physical Society.

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