1,720,980 research outputs found
Mapping Itinerant Electrons around Kondo Impurities
No full textWe investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic.Deutsche Forschungsgemeinschaft [SFB 602
Scanning tunneling spectroscopy of subsurface Ag and Ge impurities in copper
No full textAbstract We investigate single Ge and Ag impurities buried below a Cu(100) surface using low temperature scanning tunneling microscopy. The interference patterns in the local density of states are surface scattering signatures of the bulk impurities, which result from 3D Friedel oscillations and the electron focusing effect. Comparing the isoelectronic d scatterer Ag and the sp scatterer Ge allows to distinguish contributions from impurity scattering and the host. Energy-independent effective scattering phase shifts are extracted using a plane wave tight-binding model and reveal similar values for both species. A comparison with ab initio calculations suggests incoherent sp scattering processes at the Ge impurity. As both scatterers are spectrally homogeneous, scanning tunneling spectroscopy of the interference patterns yields real-space signatures of the bulk electronic structure. We find a kink around zero bias for both species that we assign to a renormalization of the band structure due to many-body effects, which can be described with a Debye self-energy and a surprisingly high electron–phonon coupling parameter λ . We propose that this might originate from bulk propagation in the vicinity of the surface.Abstract We investigate single Ge and Ag impurities buried below a Cu(100) surface using low temperature scanning tunneling microscopy. The interference patterns in the local density of states are surface scattering signatures of the bulk impurities, which result from 3D Friedel oscillations and the electron focusing effect. Comparing the isoelectronic d scatterer Ag and the sp scatterer Ge allows to distinguish contributions from impurity scattering and the host. Energy-independent effective scattering phase shifts are extracted using a plane wave tight-binding model and reveal similar values for both species. A comparison with ab initio calculations suggests incoherent sp scattering processes at the Ge impurity. As both scatterers are spectrally homogeneous, scanning tunneling spectroscopy of the interference patterns yields real-space signatures of the bulk electronic structure. We find a kink around zero bias for both species that we assign to a renormalization of the band structure due to many-body effects, which can be described with a Debye self-energy and a surprisingly high electron–phonon coupling parameter λ . We propose that this might originate from bulk propagation in the vicinity of the surface.Open-Access-Publikationsfonds 202
Structural and electronic properties of epitaxial V2O3 thin films
No full textThin films of V2O3 with thickness 4-300 nm were grown on (11 (2) over bar0)-oriented sapphire substrates by reactive dc magnetron sputtering. X-ray diffraction, pole figure measurements and scanning tunnelling microscopy show high crystallinity and epitaxy to the substrate with a faceted surface structure, and the absence of strain. Measurements of the electrical resistivity, scanning tunnelling and x-ray absorption spectroscopy show a metal-insulator transition near 150 K that is connected with the opening Of an energy gap and a characteristic modification of the absorption spectrum at the vanadium-2p and Oxygen-1 s edges. These observations reveal that the V2O3(11 (2) over bar0) films have bulk-like properties
Kondo resonance of single Co atoms embedded in Cu(111)
No full textThe Kondo resonance of single Co atoms embedded in a Cu matrix has been investigated with tunneling spectroscopy at T=8 K. Dilute magnetic alloys were prepared by homoepitaxial growth of Cu(111) films incorporating approximately 0.1% Co atoms as magnetic scattering centers. The Co impurities in the first layer of the Cu matrix show a characteristic, symmetric dip in the differential conductance around zero bias, indicating the presence of the many-body Abrikosov-Suhl resonance. The corresponding Kondo temperature is found to be T-K=405+/-35 K, which is much higher than previously reported values for Co adsorbate atoms
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Tip-Enhanced Strong-Field Photoemission
No full textNonlinear photoelectron emission from metallic nanotips is explored in the strong-field regime. The passage between the multiphoton and the optical field emission regimes is clearly identified. The experimental observations are in agreement with a quantum mechanical strong-field model.Deutsche Forschungsgemeinschaft [DFG-ZUK 45/1, SPP 1391]; E
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