The Experts below are selected from a list of 69867 Experts worldwide ranked by ideXlab platform
Ciccacci F. - One of the best experts on this subject based on the ideXlab platform.
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Cobalt atoms drive the anchoring of Co-TPP molecules to the oxygen-passivated Fe(0 0 1) surface
'Elsevier BV', 2020Co-Authors: Calloni A., Jagadeesh M. S., Bussetti G., Fratesi G., Achilli S., Picone A., Lodesani A., Brambilla A., Goletti C., Ciccacci F.Abstract:We present a multitechnique investigation of the structural and electronic properties of the prototypical system composed by ultra-thin films of magnetic molecules [Co-tetraphenyl-porphyrins (Co-TPP)] grown on a ferromagnetic substrate [oxygen passivated Fe(0 0 1), namely the Fe(0 0 1)-p(1 × 1)O surface]. Low Energy electron diffraction (LEED) and scanning tunneling microscopy (STM), coupled with first-principles calculations, reveal the formation of a commensurate superstructure at monolayer coverage, made by a square array of flat-lying TPP molecules. UV–Photoemission and inverse Photoemission spectroscopies (UPS and IPES) are used to investigate their electronic structure. Similar to our previous results on the Zn–TPP growth on Fe(0 0 1)–p(1 × 1)O, the passivation of the metallic surface is able to preserve the Photoemission features characteristic of quasi-free molecules, opening the route towards an exploitation of single oxide layers as protective films in organic/inorganic junctions. X-ray Photoemission (XPS) and near edge X-ray adsorption fine structure spectroscopies (NEXAFS), are used to reveal the details of the Co–TPP interaction with the substrate.We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support (Application No. HP10C2SVDP).Peer reviewe
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Cobalt atoms drive the anchoring of Co-TPP molecules to the oxygen-passivated Fe(0 0 1) surface
'Elsevier BV', 2019Co-Authors: Calloni A., Bussetti G., Fratesi G., Achilli S., Picone A., Lodesani A., Brambilla A., Goletti C., Jagadeesh Madan, Ciccacci F.Abstract:We present a multitechnique investigation of the structural and electronic properties of the prototypical system composed by ultra-thin films of magnetic molecules [Co-tetraphenyl-porphyrins (Co-TPP)] grown on a ferromagnetic substrate [oxygen passivated Fe(0 0 1), namely the Fe(0 0 1)-p(1 × 1)O surface]. Low Energy electron diffraction (LEED) and scanning tunneling microscopy (STM), coupled with first-principles calculations, reveal the formation of a commensurate superstructure at monolayer coverage, made by a square array of flat-lying TPP molecules. UV–Photoemission and inverse Photoemission spectroscopies (UPS and IPES) are used to investigate their electronic structure. Similar to our previous results on the Zn–TPP growth on Fe(0 0 1)–p(1 × 1)O, the passivation of the metallic surface is able to preserve the Photoemission features characteristic of quasi-free molecules, opening the route towards an exploitation of single oxide layers as protective films in organic/inorganic junctions. X-ray Photoemission (XPS) and near edge X-ray adsorption fine structure spectroscopies (NEXAFS), are used to reveal the details of the Co–TPP interaction with the substrate
Yang Wang - One of the best experts on this subject based on the ideXlab platform.
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observation of a warped helical spin texture in bi 2 se 3 from circular dichroism angle resolved Photoemission spectroscopy
Physical Review Letters, 2011Co-Authors: Yang Wang, David Hsieh, D Pilon, Liang Fu, Dillon Gardner, Nuh GedikAbstract:A differential coupling of topological surface states to left- versus right-circularly polarized light is the basis of many optospintronics applications of topological insulators. Here we report direct evidence of circular dichroism from the surface states of Bi_2Se_3 using laser-based time-of-flight angle-resolved Photoemission spectroscopy. By employing a novel sample rotational analysis, we resolve unusual modulations in the circular dichroism Photoemission pattern as a function of both energy and momentum, which perfectly mimic the predicted but hitherto unobserved three-dimensional warped spin texture of the surface states. By developing a microscopic theory of Photoemission from topological surface states, we show that this correlation is a natural consequence of spin-orbit coupling. These results suggest that our technique may be a powerful probe of the spin texture of spin-orbit coupled materials in general.
J Braun - One of the best experts on this subject based on the ideXlab platform.
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origin of spin polarized photocurrents in the topological surface states of bi 2 se 3
Physical Review B, 2018Co-Authors: A S Ketterl, J Braun, J Minar, H Ebert, Sebastian Otto, M Bastian, Beatrice Andres, Cornelius Gahl, O E Tereshchenko, K A KokhAbstract:For the generation of spin-polarized photocurrents in topological insulators, a coupling between photon angular momentum and electron spin is often assumed. Such a coupling seems to be supported by dichroism reported in $E({k}_{y})$-intensity maps in Photoemission. We show in three dimensional two-photon Photoemission and one-step Photoemission calculations that the circular dichroism is in fact threefold in $E({k}_{x},{k}_{y})$ maps although it may appear antisymmetric in $E({k}_{y})$. The threefold symmetry is inconsistent with the previously assumed coupling between photon momentum and electron's chiral spin via the orbital momentum. Instead it reflects the surface point group. The only antisymmetric patterns appear in the energy range in which surface and bulk states hybridize. In general, a threefold-symmetric dichroic signal does not support unidirectional photocurrents. Nevertheless, the residual asymmetry of up to 3.5% in our Photoemission spectra is compatible with previously observed helicity-dependent photocurrents.
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direct observation of half metallicity in the heusler compound co2mnsi
Nature Communications, 2014Co-Authors: M Jourdan, Andrei Gloskovskii, J Braun, J Minar, Alexander Kronenberg, Stanislav Chadov, Benjamin Balke, M Kolbe, H J Elmers, G SchonhenseAbstract:Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-Photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of (93(-11)(+7)) % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray Photoemission spectroscopy experiments are performed. All experimental results are compared with advanced band structure and Photoemission calculations which include surface effects. Excellent agreement is obtained with calculations, which show a highly spin polarized bulk-like surface resonance ingrained in a half metallic bulk band structure.
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correlation effects circular dichroism and fermi surfaces of bulk nickel from soft x ray angle resolved Photoemission
Physical Review B, 2012Co-Authors: J Braun, J Minar, H Ebert, A Chainani, Jun Miyawaki, Y Takata, M Taguchi, M Oura, S ShinAbstract:Within this soft x-ray Photoemission study we present a detailed experimental and theoretical view on the bulk-related electronic structure of ferromagnetic nickel. Our results resolve the long-standing issue of the Fermi surfaces of bulk Ni and thereby establish the validity of a local correlation picture for its electronic structure. We performed complementary theoretical and experimental soft x-ray angle-resolved photomission spectroscopy studies to determine the Fermi surfaces and correlation effects in the bulk states of Ni. The electronic structure, obtained from the local-spin density approximation with dynamical mean-field theory and one-step Photoemission calculations including matrix elements, is based on a fully relativistic treatment using a complex and energy-dependent self-energy $\ensuremath{\Sigma}(E)$. The experimental band dispersions, the circular dichroism in the spectral functions, and the experimentally extracted self-energy $\ensuremath{\Sigma}(E)$ are in agreement with theoretical findings.
Y Liu - One of the best experts on this subject based on the ideXlab platform.
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Photoemission circular dichroism and spin polarization of the topological surface states in ultrathin bi 2 te 3 films
Physical Review Letters, 2015Co-Authors: Iwao Matsuda, Y Liu, Ryu Yukawa, Longxiang Zhang, T Miller, T C ChiangAbstract:The complex behavior of Photoemission in topological insulators is a result of quantum interference involving three Photoemission channels according to $a\phantom{\rule{0}{0ex}}b\phantom{\rule{0.333em}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations.
Andrei Gloskovskii - One of the best experts on this subject based on the ideXlab platform.
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accurate determination of the valence band edge in hard x ray Photoemission spectra using gw theory
Journal of Applied Physics, 2016Co-Authors: Johannes Lischner, Giuseppina Conti, Andrei Gloskovskii, Slavomír Nemšák, Gunnar Karl PalssonAbstract:We introduce a new method for determining accurate values of the valence-band maximum in x-ray Photoemission spectra. Specifically, we align the sharpest peak in the valence-band region of the experimental spectrum with the corresponding feature of a theoretical valence-band density of states curve from ab initio GW theory calculations. This method is particularly useful for soft and hard x-ray Photoemission studies of materials with a mixture of valence-band characters, where strong matrix element effects can render standard methods for extracting the valence-band maximum unreliable. We apply our method to hydrogen-terminated boron-doped diamond, which is a promising substrate material for novel solar cell devices. By carrying out Photoemission experiments with variable light polarizations, we verify the accuracy of our analysis and the general validity of the method.
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direct observation of half metallicity in the heusler compound co2mnsi
Nature Communications, 2014Co-Authors: M Jourdan, Andrei Gloskovskii, J Braun, J Minar, Alexander Kronenberg, Stanislav Chadov, Benjamin Balke, M Kolbe, H J Elmers, G SchonhenseAbstract:Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-Photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of (93(-11)(+7)) % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray Photoemission spectroscopy experiments are performed. All experimental results are compared with advanced band structure and Photoemission calculations which include surface effects. Excellent agreement is obtained with calculations, which show a highly spin polarized bulk-like surface resonance ingrained in a half metallic bulk band structure.
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time of flight photoelectron spectromicroscopy of single mos2 nanotubes
Journal of Applied Physics, 2006Co-Authors: Andrei Gloskovskii, G Schonhense, S A Nepijko, Mirko Cinchetti, Gerhard H Fecher, Hem C Kandpal, Claudia Felser, Helen Annal Therese, Nicole Zink, Wolfgang TremelAbstract:There is a recent interest in nanoscale materials, in particular, nanotubes based not only on carbon. In this study, Photoemission spectra of single MoS2 nanotubes deposited on a Si surface were recorded in order to explain their electronic structure. The photoelectrons were excited by a femtosecond laser oscillator resulting in two-photon Photoemission. A spectromicroscopic technique based on imaging time-of-flight detection was used to record the spatially resolved photoelectron spectra. Self-consistent electronic structure calculations for MoS2 slabs using the full potential linear augmented plane wave method are used to explain the peculiarities of the observed spectra. It turns out that the MoS2 nanotubes are semiconducting with a band gap of about 1eV. The two-photon transitions proceed through intermediate states in a region with high density of states; this gives rise to a high Photoemission intensity.
