320 research outputs found
Data for: Light-induced hexatic phase in a layered quantum material
No full textThis dataset contains the data displayed in the publication "Light-induced hexatic state in a layered quantum material" by T. Domröse, Th. Danz, S.F. Schaible, K. Rossnagel, S.V. Yalunin and C. Ropers
Multilayer chromium based coatings grown by atmospheric pressure direct liquid injection CVD
No full textThere is a great interest for multilayer hard coatings because they exhibit enhanced properties resulting from their nanostructuration. Such coatings are frequently constituted of carbide and nitride and are generally deposited under very low pressure by plasma and PVD processes. These vacuum techniques enable the growth of heterostructures with nanometric thick individual layers and sharp interfaces, which are two requirements for advanced performances. However, both to develop more economical processes and with the goal of continuous deposition applications, the CVD processes operating under atmospheric pressure are particularly attractive. In this paper we show that the combination of pulsed direct liquid injection and the use of metalorganic precursor (DLI-MOCVD) is a promising route for the growth of nanostructured multilayer coatings under atmospheric pressure. Chromium metal as well as chromium carbide and nitrides monolithic coatings have been deposited at 773 K by this process using liquid solution of bis(benzene) chromium as Cr molecular precursor. Then, CrCx/CrN nanostructured multilayer coatings with a bilayer period as low as 50 nm have been grown. Structural characterizations and preliminary mechanical properties of these metallurgical coatings are discussed
Mobile qualified electronic signatures for secure mobile brokerage
No full textDespite a legal framework being in place for several years, the market share of qualified electronic signatures is disappointingly low. Mobile Signatures provide a new and promising opportunity for the deployment of an infrastructure for qualified electronic signatures. We that SIM-based signatures are the most secure and convenient solution. However, using the SIM-card as a secure signature creation device (SSCD) raises new challenges, because it would contain the user’s private key as well as the subscriber identification. Combining both functions in one card raises the question who will have the control over the keys and certificates. We propose a protocol called Certification on Demand (COD) that separates certification services from subscriber identification information and allows consumers to choose their appropriate certification services and service providers based on their needs. This infrastructure could be used to enable secure mobile brokerage services that can ommit the necessity of TAN lists and therefore allow a better integration of information and transaction services
Mobile qualified electronic signatures and certification on demand
No full textDespite a legal framework being in place for several years, the market share of qualified electronic signatures is disappointingly low. Mobile Signatures provide a new and promising opportunity for the deployment of an infrastructure for qualified electronic signatures. We analyzed two possible signing approaches (server based and client based signatures) and conclude that SIM-based signatures are the most secure and convenient solution. However, using the SIM-card as a secure signature creation device (SSCD) raises new challenges, because it would contain the user’s private key as well as the subscriber identification. Combining both functions in one card raises the question who will have the control over the keys and certificates. We propose a protocol called Certification on Demand (COD) that separates certification services from subscriber identification information and allows consumers to choose their appropriate certification services and service providers based on their needs. We also present some of the constraints that still have to be addressed before qualified mobile signatures are possible
80% Valley Polarization of Free Carriers in Singly Oriented Single-Layer WS2 on Au(111)
No full textWe employ time- and angle-resolved photoemission spectroscopy to study the spin- and valley-selective photoexcitation and dynamics of free carriers at the K and K′ points in singly oriented single-layer WS2/Au(111). Our results reveal that in the valence band maximum an ultimate valley polarization of free holes of 84% can be achieved upon excitation with circularly polarized light at room temperature. Notably, we observe a significantly smaller valley polarization for the photoexcited free electrons in the conduction band minimum. Clear differences in the carrier dynamics between electrons and holes imply intervalley scattering processes into dark states being responsible for the efficient depolarization of the excited electron population
Structural dynamics of incommensurate charge-density waves tracked by ultrafast low-energy electron diffraction
No full textZeitaufgelöste Photoelektronenspektroskopie an den 2D-Materialien Graphit, WS2 und WTe2
No full textIn der vorliegenden Dissertation wird die Dynamik von optisch angeregten Ladungsträgern in 2D-Materialien mittels zeit- und winkelaufgelöster Photoelektronenspektroskopie (trARPES) untersucht. Die optische Anregung von Elektronen im k-Raum unterliegt neben der Energieerhaltung gewissen Auswahlregeln, welche abhängig von der Polarisation des Anregepulses bestimmte Übergänge ausschließen, obwohl die Photonenenergie der Differenz von Anfangs- und Endzustand entspricht. Das führt dazu, dass durch die optische Anregung eine polarisationsabhängige Verteilung der angeregten Elektronen im k-Raum entsteht. Die Messmethode trARPES ermöglicht nun die direkte Beobachtung der Elektronendynamik im k-Raum. Dadurch erhält man einerseits Einblicke in den ursprünglich induzierten Nichtgleichgewichtszustand und andererseits in die darauffolgenden Relaxationsprozesse, durch welche das elektronische System die von der optischen Anregung übertragene Polarisation verliert. Die in dieser Arbeit untersuchten Proben sind die Schichtkristalle Graphit und Td-WTe2 sowie eine einfach orientierte Monolage 1H-WS2 auf Au(111). Für Graphit und die WS2- Monolage konnten Ladungsträger gezielt durch die Wahl der Polarisation des Anregepulses an bestimmten Stellen im k-Raum angeregt werden. Bei der Messung an WTe2 konnte ein solcher Effekt nicht nachgewiesen werden
Orbital- and kz -Selective Hybridization of Se 4p and Ti 3d States in the Charge Density Wave Phase of TiSe2
No full textWe revisit the enduring problem of the 2×2×2 charge density wave (CDW) order in TiSe2, utilizing photon energy-dependent angle-resolved photoemission spectroscopy to probe the full three-dimensional high- and low-temperature electronic structure. Our measurements demonstrate how a mismatch of dimensionality between the 3D conduction bands and the quasi-2D valence bands in this system leads to a hybridization that is strongly kz dependent. While such a momentum-selective coupling can provide the energy gain required to form the CDW, we show how additional "passenger" states remain, which couple only weakly to the CDW and thus dominate the low-energy physics in the ordered phase of TiSe2
Survival of Floquet-Bloch States in the Presence of Scattering
No full textFloquet theory has spawned many exciting possibilities for electronic structure control with light, with enormous potential for future applications. The experimental demonstration in solids, however, remains largely unrealized. In particular, the influence of scattering on the formation of Floquet-Bloch states remains poorly understood. Here we combine time- and angle-resolved photoemission spectroscopy with time-dependent density functional theory and a two-level model with relaxation to investigate the survival of Floquet-Bloch states in the presence of scattering. We find that Floquet-Bloch states will be destroyed if scattering - activated by electronic excitations - prevents the Bloch electrons from following the driving field coherently. The two-level model also shows that Floquet-Bloch states reappear at high field intensities where energy exchange with the driving field dominates over energy dissipation to the bath. Our results clearly indicate the importance of long scattering times combined with strong driving fields for the successful realization of various Floquet phenomena
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