Measuring correlated-electron effects with low energy alkaline earth ion scattering

He, Xiaoxiao; Yarmoff, J. A.

doi:10.1016/j.nimb.2010.10.018

Cited by 6 publications

(26 citation statements)

References 16 publications

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“…As shown by Langreth and Nordlander [34], the master equations can still be used at this point if essentially no charge is transferred during the time span the level crosses the Fermi energy. This leads to an additional criterion at z = zc-In the next section, we will see, however, that for the upper level of the Sr:Au system investigated by He and Yarmoff [30,31], the constraint (36) is violated not only at z -zc but for almost the whole trajectory. Hence, in order to analyze the correlation-driven local-moment physics possibly at work in this experiment, the solutions of the full quantum-kinetic equations are needed.…”

Section: Quantum Kineticsmentioning

confidence: 90%

“…We presented a realistically parametrized Anderson-Newns model for charge-transferring collisions between a strontium projectile and a gold target and used the model to analyze from a many-body theoretical point of view the experiment of He and Yarmoff [30,31] which indicated that in this type of surface collision, a mixed-valence resonance affects the final charge state of the projectile.…”

Section: Discussionmentioning

confidence: 99%

“…Borisov and Wille [57], on the other hand, found the level width of hydrogen ions approaching an aluminum surface to be for distances larger than five Bohr radii also not too far off the widths obtained from Gadzuk's golden rule calculation, that is, the widths are perhaps off by a factor 2. The reason most probably is Gadzuk's ingenious choice of the tunneling matrix element (see below) which takes care of the nonorthogonality of the projectile and target states [44], Since the turning point of the strontium ion is sufficiently far away from the first atomic layer, we estimate it to be around five Bohr radii, we expect Gadzuk's semiempirical approach to also provide a reasonable parametrization of the Sr: Au system investigated by He and Yarmoff [30,31]. The corrections due to chemical interactions between the strontium projectile and the gold surface, occurring at shorter distances and included in first-principles approaches [55][56][57][58][59], should not yet play a role.…”

Section: N Modelmentioning

confidence: 99%

“…10.Fk the neutralization probability of strontium ions on gold sur faces [30,31]. They found a nonmonotonous temperature de pendence of the neutralization probability which first increases and then decreases with temperature.…”

Section: Introductionmentioning

confidence: 99%

“…They found a nonmonotonous temperature de pendence of the neutralization probability which first increases and then decreases with temperature. The initial increase with temperature is most probably a thermal single-particle effect, but the latter could be the long-sought fingerprint for a transient mixed-valence resonance formed during an electron transfer from a surface to an atomic projectile [28,29], In this work, following the lead of Nordlander and co workers [28,[32][33][34] as well as Merino and Marston [29], we analyze He and Yarmoff's experiment [30,31] from a manybody theoretical point of view. In particular, we test the claim that the negative temperature dependence at high temperatures arises from the local moment of the unpaired electron in the 5,v shell of the approaching ion.…”

Section: Introductionmentioning

confidence: 99%

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Many-body theory of the neutralization of strontium ions on gold surfaces

2015

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Motivated by experimental evidence for mixed-valence correlations affecting the neutralization of strontium ions on gold surfaces, we set up an Anderson-Newns model for the Sr: Au system and calculate the neutralization probability a as a function of temperature. We employ quantum-kinetic equations for the projectile Green functions in the finite-U noncrossing approximation. Our results for a agree reasonably well with the experimental data as far as the overall order of magnitude is concerned, showing in particular the correlation-induced enhancement of a. The experimentally found nonmonotonous temperature dependence, however, could not be reproduced. Instead of an initially increasing and then decreasing a, we find over the whole temperature range only a weak negative temperature dependence. It arises, however, clearly from a mixed-valence resonance in the projectile's spectral density and thus supports qualitatively the interpretation of the experimental data in terms of a mixed-valence scenario.

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Section: Quantum Kineticsmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: N Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Many-body theory of the neutralization of strontium ions on gold surfaces

2015

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Mixed-valence correlations in charge-transferring atom–surface collisions

2015

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Motivated by experimental evidence for a mixed-valence state to occur in the neutralization of strontium ions on gold surfaces we analyze this type of charge-transferring atom-surface collision from a many-body theoretical point of view using quantum-kinetic equations together with a pseudoparticle representation for the electronic configurations of the atomic projectile. Particular attention is paid to the temperature dependence of the neutralization probability which-experimentally-seems to signal mixed-valence-type correlations affecting the charge-transfer between the gold surface and the strontium projectile. We also investigate the neutralization of magnesium ions on a gold surface which shows no evidence for a mixed-valence state. Whereas for magnesium excellent agreement between theory and experiment could be obtained, for strontium we could not reproduce the experimental data. Our results indicate mixed-valence correlations to be in principle present, but for the model mimicking most closely the experimental situation they are not strong enough to affect the neutralization process quantitatively.

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Signals of strong electronic correlation in ion scattering processes

Bonetto

González²,

Goldberg

2016

Phys. Rev. B

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Previous measurements of neutral atom fractions for Sr + scattered by gold polycrystalline surfaces show a singular dependence with the target temperature. There is still not a theoretical model that can properly describe the magnitude and the temperature dependence of the neutralization probabilities found. Here, we applied a first-principles quantum-mechanical theoretical formalism to describe the time-dependent scattering process. Three different electronic correlation approaches consistent with the system analyzed are used: (i) the spinless approach, where two charge channels are considered (Sr 0 and Sr + ) and the spin degeneration is neglected; (ii) the infinite-U approach, with the same charge channels (Sr 0 and Sr + ) but considering the spin degeneration; and (iii) the finite-U approach, where the first ionization and second ionization energy levels are considered very, but finitely, separated. Neutral fraction magnitudes and temperature dependence are better described by the finite-U approach, indicating that e-correlation plays a significant role in charge-transfer processes. However, none of them is able to explain the nonmonotonous temperature dependence experimentally obtained. Here, we suggest that small changes in the surface work function introduced by the target heating, and possibly not detected by experimental standard methods, could be responsible for that singular behavior. Additionally, we apply the same theoretical model using the infinite-U approximation for the Mg-Au system, obtaining an excellent description of the experimental neutral fractions measured.

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Measuring correlated-electron effects with low energy alkaline earth ion scattering

Cited by 6 publications

References 16 publications

Many-body theory of the neutralization of strontium ions on gold surfaces

Many-body theory of the neutralization of strontium ions on gold surfaces

Mixed-valence correlations in charge-transferring atom–surface collisions

Signals of strong electronic correlation in ion scattering processes

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