Electronic excitation as a resonant process: e<sup>-</sup>O<sub>2</sub>collisions

Teillet‐Billy, D.; Malegat, L; Gauyacq, J.P.

doi:10.1088/0022-3700/20/13/026

Cited by 70 publications

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“…This excitation mechanism is not only found in STM-induced spin flip. Similar excitation processes have been shown to be very efficient for spin-forbidden electronic excitations in electron-molecule collisions [18] or in surface processes [19], as well as for rotational IETS [20].The energy losses associated with the magnetic anisotropy in the presence of a magnetic field, B, have been modelled very efficiently in these systems [13,14] using the following Hamiltonian :Where E and D are two constants describing the effect of the environment on the spin direction, g is the gyromagnetic factor and µ B the Bohr magneton [13,14]. S is the spin operator of the adsorbate and S x,y,z its projections on the Cartesian axes.…”

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Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

2009

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The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using a strong coupling theory. The excitation process is shown to be a sudden switch between the initial state determined by the environmental anisotropy to an intermediate state given by the coupling to the tunnelling electron. This explains the observed large inelastic currents. Application is presented for Fe and Mn adsorbates on CuN monolayers on Cu(100). First-principles calculations show the dominance of one collisional channel, leading to a quantitative agreement with the experiment.PACS numbers: 68.37. Ef, The way electrons flow through atomic contacts has important fundamental and technological implications [1]. Electronic transport is a quantal process in which charge, spin and vibrational degrees of freedom are entangled leading to problems of intrinsic fundamental interest. Technologically, the quest for minutarization is pushing the limits of devices to the atomic scale, where the above transport properties will determine the actual device functionalities. An important issue is the appearance of inelastic effects where energy is taken from the electron flow into the different degrees of freedom of the system. Inelasticities lead to new regimes of transport that contain relevant information on the atomic contact and have been thus used to develop single atom and molecule spectroscopies [2,3,4].Inelastic electron tunneling spectroscopy (IETS) where electrons excite vibrations leading to conductance steps at certain voltage thresholds [2] has been extensively studied in the last years [5,6,7,8,9]. The inelastic change in conductance is within a few percent of the elastic conductance, mainly due the smallness of the electron-vibration coupling [10,11]. Recently, Heinrich and co-workers have been able to develop a spin-resolved spectroscopy using an STM [4,12,13,14]. In magnetic IETS [4], the tunneling electron yields energy to the spin of an adsorbed magnetic atom and in this way changes its orientation by overcoming the magnetic anisotropy barrier of the atom on the surface. Magnetic transitions in the meV range could be observed in adsorbates partly decoupled from a metal substrate [4,12,13,14,15]. As in vibrational IETS, the conductance presents a step at the energy threshold however the changes in conductance at inelastic threshold can reach several hundreds percent. This is at odds with previous treaments [13,16,17] where first-order perturbation theory is used.In this letter, we present an all-order theory of the spin transitions IETS and apply it to the cases of Fe and Mn adsorbates on a CuN monolayer on Cu, experimentally studied in Refs. [13,14]. We compute the relative weights of both elastic and inelastic channels, leading to a quantitative account of the inelastic currents in the experimental observations. The theory reveals the nature of the inelastic transitions and explains the extremely large inelastic currents in these magnetic systems.The general idea of our approach is the following. ...

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Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

2009

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“…For NO and NO − the Morse parameters were taken from the Refs. [26,27,28]. All the constants entering in Eq.…”

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confidence: 99%

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N₂and NO molecules

Laporta

Celiberto

Wadehra

2012

Plasma Sources Sci. Technol.

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Abstract. Electron-impact v i → v f vibrational excitations cross sections, involving rovibrationally excited N 2 (v i , J) and NO(v i , J) molecules (fixed J), are calculated for collisions occurring through the nitrogen resonant electronic state N − 2 (X 2 Π g ), and the three resonant states of nitric oxide NO − ( 3 Σ − , 1 ∆, 1 Σ + ). Complete sets of cross sections have been obtained for all possible transitions involving 68 vibrational levels of N 2 (X 1 Σ + g ) and 55 levels of NO(X 2 Π), for the incident electron energy between 0.1 and 10 eV. In order to study the rotational motion in the resonant processes, cross sections have been also computed for rotationally elastic transitions characterized by the rotational quantum number J running from 0 through 150. The calculations are performed within the framework of the local complex potential model, by using potentials energies and widths optimized in order to reproduce the experimental cross sections available in literature. Rate coefficients are calculated for all the (v i , J) → (v f , J) transitions by assuming a Maxwellian electron energy distribution function in the temperature range from 0.1 eV to 100 eV.All the produced numerical data can be accessed at

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“…20,21 In particular, the strong coupling approach yielded a physical view of the excitation mechanism and a detailed account of the great efficiency of tunneling electrons in inducing inelastic effects, as well as an account of the finite lifetime of magnetic excitations due to electron-hole pair creation; 22 this also brought forward the link between magnetic excitation and other angular momentum transfer processes in other surface and molecular physics problems. [23][24][25][26] Tunneling electrons should also be extremely efficient in inducing magnetic excitations in the case of a magnetic atom lattice, i.e., in the case of local spins coupled together via a ferromagnetic or an antiferromagnetic interaction. Several recent experimental studies have been devoted to such systems in one-dimension and for finite size; [3][4][5] they showed that indeed tunneling electrons were efficiently inducing magnetic transitions in finite size systems, in a way similar to the case of individual adsorbates.…”

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Excitation of spin waves by tunneling electrons in ferromagnetic and antiferromagnetic spin-12Heisenberg chains

Gauyacq

Lorente

2011

Phys. Rev. B

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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.

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Electronic excitation as a resonant process: e^-O₂collisions

Cited by 70 publications

References 34 publications

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N₂and NO molecules

Excitation of spin waves by tunneling electrons in ferromagnetic and antiferromagnetic spin-12Heisenberg chains

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Electronic excitation as a resonant process: e-O2collisions

Cited by 70 publications

References 34 publications

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2and NO molecules

Excitation of spin waves by tunneling electrons in ferromagnetic and antiferromagnetic spin-12Heisenberg chains

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Electronic excitation as a resonant process: e^-O₂collisions

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N₂and NO molecules