2017 
Choi, D.  J., Robles, R., Yan, S., Burgess, J. A. J., RolfPissarczyk, S., Gauyacq, J.  P., Lorente, N., Ternes, M., & Loth, S. (2017). Building Complex Kondo Impurities by Manipulating Entangled Spin Chains. Nano Lett., 17(10), 6203–6209.
Résumé: The creation of moleculelike structures in which magnetic atoms interact controllably is full of potential for the study of complex or strongly correlated systems. Here, we create spin chains in which a strongly correlated Kondo state emerges from magnetic coupling of transitionmetal atoms. We build chains up to ten atoms in length by placing Fe and Mn atoms on a Cu2N surface with a scanning tunneling microscope. The atoms couple antiferromagnetically via superexchange interaction through the nitrogen atom network of the surface. The emergent Kondo resonance is spatially distributed along the chain. Its strength can be controlled by mixing atoms of different transition metal elements and manipulating their spatial distribution. We show that the Kondo screening of the full chain by the electrons of the nonmagnetic substrate depends on the interatomic entanglement of the spins in the chain, demonstrating the prerequisites to build and probe spatially extended strongly correlated nanostructures.


2016 
Choi, D.  J., Robles, R., Gauyacq, J.  P., RubioVerdu, C., Lorente, N., & Ignacio Pascual, J. (2016). Spinpolarised edge states in atomic Mn chains supported on Cu2N/Cu (100). J. Phys. Condens. Matter., 28(23), 23lt01.
Résumé: Scanning tunnelling microscopy and density functional theory studies of manganese chains adsorbed on Cu2N/Cu (100) reveal an unsuspected electronic edge state at [Formula: see text] eV above the Fermi energy. This Tammlike state is strongly localised to the terminal Mn atoms of the chain and fully spin polarised. However, no equivalence is found for occupied states, and the electronic structure at [Formula: see text] 1 eV is mainly spin unpolarised due to the extended pstates of the N atoms that mediate the coupling between the Mn atoms in the chain. The spin polarisation of the edge state is affected by the antiferromagnetic ordering of the chains leading to nontrivial consequences.


Choi, D.  J., Robles, R., Gauyacq, J.  P., Ternes, M., Loth, S., & Lorente, N. (2016). Structural and magnetic properties of FeMnx chains (x=1–6) supported on Cu2N/Cu (100). Phys. Rev. B, 94(8), 085406.


Gauyacq, J. P., & Lorente, N. (2016). Extremely longlived magnetic excitations in supported Fe chains. Phys. Rev. B, 94(4), 045420.


2015 
Gauyacq, J.  P., & Lorente, N. (2015). Decoherencegoverned magneticmoment dynamics of supported atomic objects. J. Phys. Condens. Matter., 27(45), 455301.
Résumé: Due to the quantum evolution of molecular magnetic moments, the magnetic state of nanomagnets can suffer spontaneous changes. This process can be completely quenched by environmentinduced decoherence. However, we show that for typical small supported atomic objects, the substrateinduced decoherence does change the magneticmoment evolution but does not quell it. To be specific and to compare with experiment, we analyze the spontaneous switching between two equivalent magnetization states of atomic structures formed by Fe on Cu2N/Cu (1 0 0), measured by Loth et al (2012 Science 335 1969). Due to the substrateinduced decoherence, the Rabi oscillations proper to quantum tunneling between magnetic states are replaced by an irreversible decay of long characteristic times leading to the observed stochastic magnetization switching. We show that the corresponding switching rates are small, rapidly decreasing with system's size, with a 1/T thermal behavior and in good agreement with experiments. Quantum tunneling is recovered as the switching mechanism at extremely low temperatures below the muK range for a sixFeatom system and exponentially lower for larger atomic systems. The unexpected conclusion of this work is that experiments could detect the switching of these supported atomic systems because their magnetization evolution is somewhere between complete decoherenceinduced stability and unobservably fast quantumtunneling switching.


2014 
Gauyacq, J.  P., & Lorente, N. (2014). Excitation of bondalternating spin1/2 Heisenberg chains by tunnelling electrons. J. Phys. Condens. Matter., 26(39), 394005.
Résumé: Inelastic electron tunneling spectra (IETS) are evaluated for spin1/2 Heisenberg chains showing different phases of their spin ordering. The spin ordering is controlled by the value of the two different Heisenberg couplings on the two sides of each of the chain's atoms (bondalternating chains). The perfect antiferromagnetic phase, i.e. a unique exchange coupling, marks a topological quantum phase transition (TQPT) of the bondalternating chain. Our calculations show that the TQPT is recognizable in the excited states of the chain and hence that IETS is in principle capable of discriminating the phases. We show that perfectly symmetric chains, such as closed rings mimicking infinite chains, yield the same spectra on both sides of the TQPT and IETS cannot reveal the nature of the spin phase. However, for finite size open chains, both sides of the TQPT are associated with different IETS spectra, especially on the edge atoms, thus outlining the transition.


Gauyacq, J. P., & Lorente, N. (2014). Classical limit of a quantal nanomagnet in an anisotropic environment. Surface Science, 630, 325–330.


Kepenekian, M., Gauyacq, J.  P., & Lorente, N. (2014). Difficulties in the ab initio description of electron transport through spin filters. J. Phys. Condens. Matter., 26(10), 104203.
Résumé: Spintransport calculations present certain difficulties which are sometimes overlooked when using densityfunctional theory (DFT) to analyze and predict the behavior of molecularbased devices. We analyze and give examples of some caveats of spintronic calculations using DFT. We first describe how the brokensymmetry problem of DFT can cause serious problems in the evaluation of the spin polarization of electron currents. Next, we signal the lowenergy scale of magnetic excitations, which makes them ubiquitous at already rather small biases. The existence of excitations in spin transport has catastrophic consequences in the reliability of the usual transport calculations. Finally, we compare DFT and configurationinteraction calculations of a ferrocenebased double decker that has been heralded as a possible spinfilter, and we cast a word of caution when we show that DFT is qualitatively wrong in the description of both the ground state and the excited states of ferrocene double deckers.


Kossler, S., Feulner, P., & Gauyacq, J.  P. (2014). Electronic excitations of helium bilayers on a metal substrate. Phys. Rev. B, 89(16), 165410.


2013 
Gauyacq, J. P., & Lorente, N. (2013). Magnetic reversal of a quantum nanoferromagnet. PRB, 87(19), 195402.


Gauyacq, J. P., Yaro, S. M., Cartoixa, X., & Lorente, N. (2013). CorrelationMediated Processes for ElectronInduced 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 electroninduced switching between the Neel states. Good agreement is found with the experiment, permitting us to identify three switching mechanisms: (i) low STM voltage direct electroninduced transitions, (ii) intermediate STM voltage switching via spinwavelike excitation, and (iii) high STM voltage transitions mediated by domainwall formation. Spin correlations in the antiferromagnetic chains are the switching driving force, leading to a marked chainsize dependence. DOI: 10.1103/PhysRevLett.110.087201


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.


2012 
Gauyacq, J.  P., Lorente, N., & Dutilh Novaes, F. (2012). Excitation of local magnetic moments by tunneling electrons. Prog. Surf. Sci., 87(58), 63–107.
Résumé: The advent of millikelvin 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 singularlike behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis: perturbation theories, suddenapproximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, manybody 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 electronhole pair creation in deexciting 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. (C) 2012 Elsevier Ltd. All rights reserved.


Gauyacq, J. P., & Lorente, N. (2012). Lifetime of magnetic excitations in supported ferromagnetic and antiferromagnetic spin1/2 Heisenberg chains. PHYSICAL REVIEW B, 85(11), 115420.
Résumé: The lifetime of magnetic excitations in finite 1Dsupported Heisenberg chains of magnetic atoms is studied theoretically for a model system formed of S = 1/2 spins. Both ferromagnetic and antiferromagnetic cases are considered as well as open chains and rings of atoms. Different chain lengths are considered allowing extrapolation to infinite chains. All the excited magnetic states in the finite chains and rings are studied, not only the spinwave mode. The magnetic excitations decay by electronhole pair creation in the substrate. As the main result, for all the systems considered, the decay rate appears to vary approximately proportionally to the excitation energy of the state, with a proportionality constant independent of the strength of the Heisenberg exchange term. In certain finite systems, a stable state is evidenced at low energy, associated with a special spin coupling structure.


Korytar, R., Lorente, N., & Gauyacq, J.  P. (2012). Manybody effects in magnetic inelastic electron tunneling spectroscopy. Phys. Rev. B, 85(12), 125434.
Résumé: Magnetic inelastic electron tunneling spectroscopy (IETS) shows sharp increases in conductance when a new conductance channel associated with a change in magnetic structure is open. Typically, the magnetic moment carried by an adsorbate can be changed by collision with a tunneling electron; in this process the spin of the electron can flip or not. A previous oneelectron theory [Phys. Rev. Lett. 103, 176601 (2009)] successfully explained both the conductance thresholds and the magnitude of the conductance variation. The elastic spin flip of conduction electrons by a magnetic impurity leads to the wellknown Kondo effect. In the present work, we compare the theoretical predictions for inelastic magnetic tunneling obtained with a oneelectron approach and with a manybody theory including Kondolike phenomena. We apply our theories to a singlettriplet transition model system that contains most of the characteristics revealed in magnetic IETS. We use two selfconsistent treatments (noncrossing approximation and selfconsistent ladder approximation). We show that, although the oneelectron limit is properly recovered, new intrinsic manybody features appear. In particular, sharp peaks appear close to the inelastic thresholds; these are not localized exactly at thresholds and could influence the determination of magnetic structures from IETS experiments. Analysis of the evolution with temperature reveals that these manybody features involve an energy scale different from that of the usual Kondo peaks. Indeed, the manybody features perdure at temperatures much larger than the one given by the Kondo energy scale of the system.


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). Momentumresolved electron dynamics of imagepotential 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 imagepotential state of clean and raregas covered Ag(111), Cu(111), and Cu(100) surfaces on their momentum parallel to the surface has been studied experimentally by means of timeand angleresolved twophoton photoemission spectroscopy (2PPE) and theoretically by calculations based on the manybody theory within the selfenergy 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 imagepotential 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 imagepotential states from the metal surface upon adsorption of raregas 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.


2011 
DiazTendero, S., Borisov, A. G., & Gauyacq, J.  P. (2011). Theoretical study of the electronic excited states in ultrathin ionic layers supported on metal surfaces: NaCl/Cu(111). Phys. Rev. B, 83(11), 115453.
Résumé: We present a theoretical study of the electronic excited states in ultrathin ionic layers supported on metal surfaces. We have studied 1, 2, 3, and 4 monolayers of NaCl on a Cu(111) surface. Energies, lifetimes, and associated wave functions of the excited states have been obtained with a joint, model potentialwave packet propagation approach. The excited state with the lowest energy has the character of an image potential state repelled from the surface by the NaCl layer. The next two states present a mixed character of image potential states and NaCl layer states corresponding to the quantization of the conduction band in the finitesize layer. We discuss the role of the layer thickness in decoupling these states from the metal surface and how it affects their lifetime.


Gauyacq, J. P., & Lorente, N. (2011). Excitation of spin waves by tunneling electrons in ferromagnetic and antiferromagnetic spin1/2 Heisenberg chains. PHYSICAL REVIEW B, 83(3), 035418.
Résumé: 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.


Gauyacq, J. P., & Lorente, N. (2011). Magnetic excitation by tunneling electrons of frustrated ferromagnetic spin1/2 chains and rings. PHYSICAL REVIEW B, 84(8), 085415.
Résumé: Excitation of finite size chains of magnetic spin1/2 atoms adsorbed on a surface by tunneling electrons from a scanning tunneling microscope is studied theoretically in the case of a frustrated ferromagnetic structure of the chain. The magnetic excitation processes are described using the strong coupling approach from Lorente and Gauyacq [Phys. Rev. Lett. 103, 256802 (2009)]. Varying the exchangecoupling parameters, the chain length and the strength of an applied magnetic field generates a broad variety of magnetic structures in the chain. The links between these various structures and the excitation processes by tunneling electrons are presented, together with a discussion on how the magnetic structure of a chain could be inferred from an inelastic electron tunneling experiment. Extrapolation of the finite size calculations to infinite chains leads to a discussion of the characteristics of the spin waves that can be excited by tunneling electrons in these frustrated magnetic systems.


2010 
Gauyacq, J.  P., Novaes, F. D., & Lorente, N. (2010). Magnetic transitions induced by tunneling electrons in individual adsorbed Mphthalocyanine molecules (M=Fe and Co). Phys. Rev. B, 81(16), 165423.
Résumé: We report on a theoretical study of magnetic transitions induced by tunneling electrons in individual adsorbed MPhthalocyanine (MPc) molecules where M is a metal atom: FePc on a Cu(110)(2 x 1)O surface and CoPc layers on Pb(111) islands. The magnetic transitions correspond to the change in orientation of the spin angular momentum of the metal ion with respect to the surroundings and possibly an applied magnetic field. The adsorbed FePc system is studied with a densityfunctionaltheorytransport approach showing that (i) the magnetic structure of the Fe atom in the adsorbed FePc is quite different from that of the free Fe atom or of other adsorbed Fe systems and (ii) that injection of electrons (holes) into the Fe atom in the adsorbed FePc molecule dominantly involves the Fe 3d(z)2 orbital. These results fully specify the magnetic structure of the system and the process responsible for magnetic transitions. The dynamics of the magnetic transitions induced by tunneling electrons is treated in a strongcoupling approach. The FePc treatment is extended to the CoPc case. The present calculations accurately reproduce the strength of the magnetic transitions as observed by magnetic inelastic electron tunneling spectroscopy experiments; in particular, the dominance of the inelastic current in the conduction of the adsorbed MPc molecule is accounted for.


Novaes, F. D., Lorente, N., & Gauyacq, J.  P. (2010). Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100). Phys. Rev. B, 82(15), 155401.
Résumé: The lifetimes of spin excitations of Mn adsorbates on CuN/Cu(100) are computed from first principles. The theory is based on a strongcoupling approach that evaluates the decay of a spin excitation due to electronhole pair creation. Using a previously developed theory [Phys. Rev. Lett. 103, 176601 (2009) and Phys. Rev. B 81, 165423 (2010)], we compute the excitation rates by a tunneling current for all the Mn spin states. A rate equation approach permits us to simulate the experimental results by Loth and coworkers (Nat. Phys. 6, 340 (2010)] for large tunneling currents, taking into account the finite population of excited states. Our simulations give us insight into the spin dynamics, in particular, in the way polarized electrons can reveal the existence of an excitedstate population. In addition, it reveals that the excitation process occurs in a way very different from the deexcitation one. Indeed, while excitation by tunneling electrons proceeds via the s and p electrons of the adsorbate, deexcitation mainly involves the d electrons.


Steeb, F., Mathias, S., Wiesenmayer, M., Fischer, A., Aeschlimann, M., Bauer, M., & Gauyacq, J. P. (2010). Probing adsorbate dynamics with chirped laser pulses in a singlepulse scheme. PHYSICAL REVIEW B, 82(16), 165430.
Résumé: Femtosecond dynamics of the modellike adsorption system Cs/Cu(111) is probed by twophoton photoelectron spectroscopy (2PPE) using phasemodulated (chirped) laser pulses. The experimental data are quantitatively modeled within a wavepacket propagation approach under explicit consideration of the adsorbate motion. The results enable us to assign characteristic chirpedpulse 2PPE features to the ultrafast adsorbate dynamics associated with the excited state lifetime and the adsorbate motion, and to improve on the qualitative interpretation of experimental data as published in Petek et al. [J. Phys. Chem. A 104, 10234 (2000)]. Our results show that nonlinear photoemission with a chirped pulse in a singlepulse scheme can complement realtime studies based on pumpprobe schemes to gain quantitative insights into the femtosecond dynamics of ultrafast surface processes.


2009 
DiazTendero, S., Borisov, A. G., & Gauyacq, J.  P. (2009). Extraordinary electron propagation length in a metallic double chain supported on a metal surface. Phys. Rev. Lett., 102(16), 166807.
Résumé: The present theoretical study shows that a double chain of Cu metal atoms adsorbed on a Cu(111) metal surface can guide an excited electron for distances exceeding 10 nm. The nanostructure appears to be quasidecoupled from the substrate and thus to act as a nanowire. The origin of the above phenomenon is the interference between the decay of the quasistationary 1D spband states localized on each chain. This allows to approach the situation of the formation of bound states in the continuum first discussed in quantum systems by von Neumann and Wigner.


DiazTendero, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J.  P. (2009). Excited electron dynamics in Cu nanowires supported on a Cu(111) surface. Phys. Rev. B, 79(11), 115438.
Résumé: We present a theoretical study of the excited electron dynamics in infinite Cu monoatomic chains (nanowires) supported on a Cu(111) surface. A joint approach based on the wave packet propagation and the density functional theory is used. The nanowireinduced potential obtained from ab initio density functional theory calculations serves as an input for the wavepacket propagation study of the excited electron dynamics. The energy dispersion and the lifetime of an unoccupied onedimensional (1D) nanowirelocalized electronic band with sp character are obtained. From the group velocity and lifetime of the 1D spband states, it follows that an excited electron can travel about four to five atomic sites along the nanowire before its escape into the bulk. We show that the surface projected band gap and the surface Brillouin zone backfolding of the substrate states play a fundamental role in the lifetime of the nanowirelocalized states.


Gauyacq, J. P., DiazTendero, S., & Borisov, A. G. (2009). Mapping of the electron transmission through the wall of a quantum corral. Surf. Sci., 603(13), 2074–2081.
Résumé: We report on a theoretical study of the escape of confined surface states electrons from quantum corrals made of Cu adatoms on a Cu(1 1 1) surface. This study maps electron transmission through the corral wall and provides an extension of our earlier work focused on confinement in Cu corrals [S. DiazTendero, F.E. Olsson, A.G. Borisov, J.P. Gauyacq, Phys. Rev. B 77 (2008) 205403]. The existence of two decay modes for the confined surface state is stressed: (i) nonresonant tunnelling through the corral wall concentrated on the Cu adatoms and (ii) a resonantinduced decay involving the transient formation of a resonant state localized on top of the corral wall. The present mapping of the electron transmission reveals how the interference between the two decay modes works: there exist regions where the electron leaves the corral, balanced by regions where it enters the corral, though the global behaviour of the quasistationary states is electron escape from the corral. (C) 2009 Elsevier B.V. All rights reserved.


Lorente, N., & Gauyacq, J.  P. (2009). Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy. Phys. Rev. Lett., 103(17), 176601.
Résumé: The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using strong coupling theory. Recent measurements [Heinrich et al., Science 306, 466 ( 2004)] reveal that electron currents in a magnetic system efficiently excite its magnetic moments. Our theory shows that the incoming electron spin strongly couples with that of the adsorbate so that memory of the initial spin state is lost, leading to large excitation efficiencies. Firstprinciples transmissions are evaluated in quantitative agreement with the experiment.


2008 
Borisov, A. G., Sametoglu, V., Winkelmann, A., Kubo, A., Pontius, N., Zhao, J., Silkin, V. M., Gauyacq, J. P., Chulkov, E. V., Echenique, P. M., & Petek, H. (2008). Pi resonance of chemisorbed alkali atoms on noble metals. Phys. Rev. Lett., 101(26), 266801.
Résumé: We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle and timeresolved twophoton photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known sigma resonance oriented along the surface normal, there exist longlived alkalilocalized resonances oriented parallel to the surface (pi symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.


DiazTendero, S., Foelsch, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J.  P. (2008). Electron propagation along Cu nanowires supported on a Cu(111) surface. Nano Lett., 8(9), 2712–2717.
Résumé: We present a joint experimentaltheoretical study of the onedimensional band of excited electronic states with sp character localized on Cu nanowires supported on a Cu(111) surface. Energy dispersion and lifetime of these states have been obtained, allowing the determination of the mean distance traveled by an excited electron along the nanowire before it escapes into the substrate. We show that a Cu nanowire supported on a Cu(111) surface can guide a onedimensional electron flux over a short distance and thus can be considered as a possible component for nanoelectronics devices.


DiazTendero, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J.  P. (2008). Theoretical study of electron confinement in Cu corrals on a Cu(111) surface. Phys. Rev. B, 77(20), 205403.
Résumé: We present a theoretical study of the energies, lifetimes, wave functions, and decay paths of the excited electronic states in corral structures formed by Cu adatoms on the Cu(111) surface. Three different corrals with 35, 48, and 70 Cu adatoms have been studied within a joint approach including the density functional theory and wave packet propagation. Confinement of the electronic surface state inside the corral structure leads to the formation of welldefined resonances in the density of electronic states. Particular emphasis is given in the present work to the role of excited electronic states localized on the ring of Cu adatoms forming the corral. While never discussed in the past for corral structures, these states are equivalent to the onedimensional sp band of Cu atomic chains assembled on the Cu(111) surface that has been recently studied thoroughly. The coupling between the confined surface state resonances and the sp state localized on the Cu ring have been studied in detail. It is shown that the sp state localized on the corral wall appears as a strong perturbation in the spectrum of confined states.


Gauyacq, J.  P., Borisov, A. G., & Kazansky, A. K. (2008). Theoretical study of excited electronic states at surfaces, link with photoemission and photodesorption experiments. In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012009).
Résumé: Excited electronic states at surfaces play a very important role in a variety of surface processes. These excited states have a finite lifetime due to electrontransfer processes and their efficiency as reaction intermediates depends crucially on their lifetime. A review of several physical situations, where an excited electronic state localized on an atom interacting with a metal surface intervenes in a surface process, is presented with an emphasis on the way the metal electronic structure influences the excited state dynamics. Examples are chosen among the alkali/metal systems, stressing how the same transient electronic state can influence different dynamical processes.


Gauyacq, J. P. (2008). Laserinduced photodesorption in the Na/Cu(111) system. SURFACE SCIENCE, 602(22), 3477–3483.
Résumé: Desorption in the Na/Cu(111) system induced by an electronic excitation is studied using a quantal approach. The system is excited by a laser pulse in the fs range to the Na state corresponding to the transient capture of an electron by the alkali adsorbate. The present quantal approach describes on an equal footing the laserinduced vibrational excitation of the adsorbate in the adsorption well and the photodesorption process. It confirms earlier results using a semiclassical input. It also allows a discussion of the photodesorption probability with the photon energy: the maximum of the desorption probability per absorbed photon occurs offresonance in the highenergy wing of the electronic transition. This feature is related to the dynamics of the laserinduced process. (C) 2008 Elsevier B.V. All rights reserved.


2007 
Rousseau, P., Khemliche, H., Borisov, A. G., & Roncin, P. (2007). Quantum scattering of fast atoms and molecules on surfaces. PHYSICAL REVIEW LETTERS, 98(1), 016104.
Résumé: We present evidence for the diffraction of light keV atoms and molecules grazingly scattered on LiF(001) and NaCl(001) surfaces. At such energies, the de Broglie wavelength is 2 orders of magnitude smaller that the mean thermal atomic displacement in the crystal. Thus, no coherent scattering was expected and interaction of keV atoms with surfaces is routinely treated with classical mechanics. We show here that welldefined diffraction patterns can be observed indicating that, for grazing scattering, the pertinent wavelength is that associated with the slow motion perpendicular to the surface. The experimental data are well reproduced by an ab initio calculation.


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 BBEAM 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 timeofflight 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 electronbihole 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.


Roncin, P., Borisov, A. G., Khemliche, H., Momeni, A., Mertens, A., & Winter, H. (2002). Evidence for F formation by simultaneous doubleelectron capture during scattering of F+ from a LiF(001) surface. PHYSICAL REVIEW LETTERS, 89(4), 043201.
Résumé: Slow F+ ions (v<0.1 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence exhibit a high probability for forming F ions in the reflected beam, whereas no negative ions are found for neutral F0 projectiles. From detailed studies of projectile energy loss and charge transfer, we find evidence for a correlated doubleelectron capture process in the formation of the F ions.


2001 
Khemliche, H., Villette, J., Borisov, A. G., Momeni, A., & Roncin, P. (2001). Electron bihole complex formation in neutralization of Ne+ on LiF(001). PHYSICAL REVIEW LETTERS, 86(25), 5699–5702.
Résumé: Neutralization of low keV Ne+ ions at a LiF(001) surface is studied in a grazing incidence geometry. The combination of energy loss and electron spectroscopy in coincidence reveals two neutralization channels of comparable importance. Besides the Anger process, the Nef neutralization can proceed via peculiar target excitation, corresponding to the formation of an electron bihole complex termed trion.


Roncin, P., Khemliche, H., Momeni, A., & Borisov, A. G. (2001). Translational spectroscopy in grazing collisions on insulators. The importance of the transient negative ion and of target excitations. In PHOTONIC (pp. 571–579).
Résumé: Energy loss spectroscopy is applied to grazing collisions of keV ions on insulator surfaces. For W projectiles, analyzing in coincidence the energy loss, the final charge state and the secondary electrons, the role of the intermediate negative ions formed on the surface is outlined. The study is extended to other projectiles to probe the influence of the projectile affinity level.


2000 
Villette, J., Borisov, A. G., Khemliche, H., Momeni, A., & Roncin, P. (2000). Subsurfacechannelinglike energy loss structure of the skipping motion on an ionic crystal. PHYSICAL REVIEW LETTERS, 85(15), 3137–3140.
Résumé: The skipping motion of Ne+ ions in grazing scattering from the LiF(001) surface is studied for velocity below 0.1 a.u. with a timeofflight technique. It is demonstrated that suppression of electronic excitation and dominance of optical phonon excitation in the projectile stopping results in an odd 1,3, 5,... progression of the energy loss peaks, a feature usually ascribed to subsurface channeling. The experimental findings are well reproduced by parameterfree model calculations where thermal vibrations are the dominant cause for the ion trapping and detrapping.

