References of "Burgdörfer, Joachim"
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See detailTowards an ab initio description of the charge transfer between a proton and a lithium fluoride surface: A quantum chemistry approach
Tiwald, Paul; Gräfe, Stefanie; Burgdörfer, Joachim et al

in Nuclear Instruments and Methods in Physics Research B (2013), 317, Part A

We study the non-adiabatic charge transfer dynamics during the collision of a slow proton with a lithium fluoride surface employing a quantum-chemistry based dynamics approach. The surface is modeled by ... [more ▼]

We study the non-adiabatic charge transfer dynamics during the collision of a slow proton with a lithium fluoride surface employing a quantum-chemistry based dynamics approach. The surface is modeled by an Li5F1+ H+ cluster embedded in a large matrix of point charges. Going beyond the adiabatic (or Born–Oppenheimer) approximation, we apply multi-reference configuration-interaction methods that allow for the calculation of ground and excited states of the embedded cluster as well as of the non-adiabatic couplings between them. This information serves as input for the determination of the neutralization probability of a proton scattered off a LiF surface using Tully’s semi-classical surface hopping algorithm. [less ▲]

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See detailTransport through open quantum dots: Making semiclassics quantitative
Brezinova, Iva; Wirtz, Ludger UL; Rotter, Stefan et al

in Physical Review. B, Condensed Matter and Materials Physics (2010), 81(12),

We investigate electron transport through clean open quantum dots (quantum billiards). We present a semiclassical theory that allows to accurately reproduce quantum-transport calculations. Quantitative ... [more ▼]

We investigate electron transport through clean open quantum dots (quantum billiards). We present a semiclassical theory that allows to accurately reproduce quantum-transport calculations. Quantitative agreement is reached for individual energy-dependent and magnetic field dependent elements of the scattering matrix. Two key ingredients are essential: (i) inclusion of pseudopaths which have the topology of linked classical paths resulting from diffraction in addition to classical paths and (ii) a high-level approximation to diffractive scattering. Within this framework of the pseudopath semiclassical approximation (PSCA), typical shortcomings of semiclassical theories such as violation of the anticorrelation between reflection and transmission and the overestimation of conductance fluctuations are overcome. Beyond its predictive capabilities the PSCA provides deeper insights into the quantum-to-classical crossover. [less ▲]

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See detailRumpling of LiF(001) surface from fast atom diffraction
Schueller, A.; Wethekam, S.; Blauth, D. et al

in Physical Review. A (2010), 82(6), 062902

Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces ... [more ▼]

Quantum diffraction of fast atoms scattered from the topmost layer of surfaces under grazing angles of incidence can be employed for the analysis of detailed structural properties of insulator surfaces. From comparison of measured and calculated diffraction patterns we deduce the rumpling of the topmost surface layer of LiF(001) (i.e., an inward shift of Li(+) ions with respect to F(-) ions). The effect of thermal vibrations on the measurement of rumpling is accounted for by ab initio calculations of the mean-square vibrational amplitudes of surface ions. At room temperature this leads to a reduction of the apparent rumpling by 0.008 angstrom. We then obtain a rumpling of ( 0.05 +/- 0.04) angstrom, which improves its accuracy achieved in previous work. [less ▲]

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See detailVanishing gap in LiF for electronic excitations by slow antiprotons
Solleder, Beate; Wirtz, Ludger UL; Burgdörfer, Joachim

in Physical Review B (2009), 79(12),

We study the influence of antiprotons and protons traveling through LiF on the band structure of the insulator using the embedded-cluster method. The crystal is represented by F(m)(-)Li(n)(+) clusters ... [more ▼]

We study the influence of antiprotons and protons traveling through LiF on the band structure of the insulator using the embedded-cluster method. The crystal is represented by F(m)(-)Li(n)(+) clusters with up to 19 fluorine ions embedded in a lattice of point charges representing the remainder of the crystal. The minimum excitation energy of LiF perturbed by the (anti)proton impurity is calculated employing the multiconfiguration self-consistent field method. The repulsive potential of the antiproton causes a dramatic local perturbation of the LiF band structure. We find a strong suppression of the excitation energy by more than an order of magnitude compared to that of the unperturbed crystal. The present results provide a simple explanation of recent stopping-power experiments for antiprotons in LiF which, surprisingly, found a "metal-like" behavior of the wide-band-gap insulator LiF. Our results also agree with recent experimental data indicating a deviation from metallic behavior of the stopping power of proton projectiles. [less ▲]

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See detailFast-Atom Diffraction at Surfaces
Aigner, F.; Simonovic, N.; Solleder, B. et al

in Journal of Physics: Conference Series (2009), 194

Fast helium atoms diffracted at alkali-halide surfaces under grazing angles of incidence exhibit intriguing diffraction patterns. The persistence of quantum coherence is remarkable, considering high ... [more ▼]

Fast helium atoms diffracted at alkali-halide surfaces under grazing angles of incidence exhibit intriguing diffraction patterns. The persistence of quantum coherence is remarkable, considering high surface temperatures and high (keV) kinetic energies of the incident atoms. Dissipative and decohering effects such as the momentum transfer between the incident helium atoms and the surface influence the diffraction patterns and control the width of the diffraction peaks, but they are weak enough to preserve the visibility of the diffration patterns. We perform an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the < 110 > direction. Our results agree well with recent experimental diffraction data. [less ▲]

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See detailDiffractive paths for weak localization in quantum billiards
Brezinova, Iva; Stampfer, Christoph; Wirtz, Ludger UL et al

in Physical Review B (2008), 77(16),

We study the weak-localization effect in quantum transport through a clean ballistic cavity with regular classical dynamics. We address the question which paths account for the suppression of conductance ... [more ▼]

We study the weak-localization effect in quantum transport through a clean ballistic cavity with regular classical dynamics. We address the question which paths account for the suppression of conductance through a system where disorder and chaos are absent. By exploiting both quantum and semiclassical methods, we unambiguously identify paths that are diffractively backscattered into the cavity (when approaching the lead mouths from the cavity interior) to play a key role. Diffractive scattering couples transmitted and reflected paths and is thus essential to reproduce the weak-localization peak in reflection and the corresponding antipeak in transmission. A comparison of semiclassical calculations featuring these diffractive paths yields good agreement with full quantum calculations and experimental data. Our theory provides system-specific predictions for the quantum regime of few open lead modes and can be expected to be relevant also for mixed as well as chaotic systems. [less ▲]

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See detailSuppression of Decoherence in Fast-Atom Diffraction at Surfaces
Aigner, F.; Simonovic, N.; Solleder, B. et al

in Physical Review Letters (2008), 101(25),

Scattering of fast neutral atoms with keV kinetic energies at alkali-halide surfaces under grazing angles displays intriguing diffraction patterns. The surprisingly strong persistence of quantum coherence ... [more ▼]

Scattering of fast neutral atoms with keV kinetic energies at alkali-halide surfaces under grazing angles displays intriguing diffraction patterns. The surprisingly strong persistence of quantum coherence despite the impulsive interaction with an environment at solid state density and elevated temperatures raises fundamental questions such as to the suppression of decoherence and of the quantum-to-classical crossover. We present an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the < 110 > direction and compare with recent experimental diffraction data. From the quantitative reconstruction of diffraction images the vertical LiF-surface reconstruction, or buckling, can be determined. [less ▲]

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See detailInfluence of Inelastic Processes on Fast-Atom-Surface Diffraction
Aigner, F.; Simonovic, N.; Solleder, B. et al

in Journal of Physics: Conference Series (2008), 133

Diffraction of fast helium atoms at alkali-halide surfaces under grazing angles of incidence shows intriguing diffraction patterns. The persistence of quantum coherence is remarkably strong, even though ... [more ▼]

Diffraction of fast helium atoms at alkali-halide surfaces under grazing angles of incidence shows intriguing diffraction patterns. The persistence of quantum coherence is remarkably strong, even though high surface temperatures and high (keV) kinetic energies of the incident atoms would strongly suggest the dominance of dissipative and decohering processes. The main source of decoherence is the excitation or absorption of surface vibrations upon impact. The momentum transfer between the surface and the incident helium atom depends on the amplitude of the thermal vibrations of the surface atoms and the energy of the incident particle. We present an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the < 110 > direction, and compare with recent experimental diffraction data. [less ▲]

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See detailExcitation energy and pair correlation function of trions near an LiF surface
Solleder, Beate; Wirtz, Ludger UL; Burgdörfer, Joachim

in Physical Review B (2008), 78(15),

We investigate the excitation spectrum of a singly charged LiF surface using an embedded cluster approach. The spectrum is determined by multiconfiguration self-consistent field calculations. We find ... [more ▼]

We investigate the excitation spectrum of a singly charged LiF surface using an embedded cluster approach. The spectrum is determined by multiconfiguration self-consistent field calculations. We find stable trionic states, i.e., quasimolecular states of a three-quasiparticle complex consisting of two holes and one electron interacting through the Coulomb potential. The excitation energy of the lowest trionic state is approximately 12.1 eV. The mean hole-hole spacing is about 7.6 a.u. (or 4 A). Our results confirm the interpretation of experiments [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)] where trion excitation was suggested as effective energy-loss channel during the neutralization of Ne(+) ions at an LiF surface. [less ▲]

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See detailElectron emission from surfaces induced by HCI and lasers
Lemell, C.; Tong, X. M.; Tokesi, K. et al

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2005), 235

Electron emission from surfaces due to interaction with charged particles and electromagnetic fields is a topic of research for over 100 years. In the past decade new developments in the production of ... [more ▼]

Electron emission from surfaces due to interaction with charged particles and electromagnetic fields is a topic of research for over 100 years. In the past decade new developments in the production of ultrashort laser pulses (tau < 10 fs at a wavelength of lambda approximate to 750 nm) and of slow highly charged ions (HCI) have rendered these interactions to be remarkably similar. The description of electron emission in HO-surface interactions can therefore be transcribed to model and understand photoemission from surfaces interacting with ultrashort laser pulses. Examples will be presented for two model systems. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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