1,721,051 research outputs found
Terahertz and optical response of novel quantum materials
Full text linkQuantum materials are a class of systems that host low energy emergent properties due to the strong correlations between the lattice, charge, spin and orbital degrees of freedom. In recent years, this classification has encompassed the world of strongly correlated materials, like high-temperature superconductors and Mott-Hubbard insulators, and the topological states of matter, like Dirac/Weyl semimetals and topological insulators. This doctoral thesis discusses the study of the optical characterization of novel quantum materials, with a special focus on the terahertz (THz) spectral range, where low energy emergent features arise as a consequence of strong electronic correlations, symmetry breaking and/or topological transitions. The low energy photons associated to THz radiation grant an easy access to the quasiparticles occupying the low energy modes of quantum materials. The recent progress in the generation and detection of THz radiation have enabled the production of ultrashort pulses at the picosecond scale and their exploitation in time-domain spectroscopy measurements, like pump-probe and nonlinear spectroscopy, from which it is possible to study the out-of-equilibrium dynamics of electrons and dipole-coupled low energy states, along with the appearance of nonlinear responses at the presence of high external electric fields. This thesis shows that quantum materials can host a plethora of THz-related responses which can be tuned in terms of their thickness, temperature and external drivings, like the perturbation associated to an ultrashort optical pulse. It addresses the optical and THz study of novel magnetic quantum materials like Co2MnGa, a magnetic nodal line semimetal, MnBi2Te4, the first intrinsic magnetic topological insulator discovered, and CrI3, a layered ferromagnetic insulator with research interests ranging from spintronics to topological Majorana modes. In particular, the interplay between the magnetic, electronic and phononic states is addressed through linear and nonlinear spectroscopy, along with the direct sampling of the topological features by optical means. As a final purpose, this thesis also reports the novel findings for the direct optical sampling of the superconductive gap in the Sr-doped nickelate NdNiO2, a strain-induced superconductor. The results show how the electrodynamic properties of this material are quantitatively different from the ones found in cuprate superconductors, sharing a similar infinite layer structural phase
Organometallics on silicon: A synchrotron radiation photoemission study of the adsorption of iron pentacarbonyl on Si(111) surfaces with different reconstructions
No full textORGANOMETALLIC ADSORPTION ON SEMICONDUCTORS - A SYNCHROTRON RADIATION PHOTOEMISSION-STUDY OF FERROCENE AND NICKELOCENE ON SI(111)2X1
No full textCHEMISORPTION AND PHYSISORPTION OF SIMPLE ALCOHOLS ON CLEAVED SILICON
No full textWe investigated the adsorption properties of methanol and ethanol on Si(111)2 x 1 as a function of temperature in the range 80-300 K by means of synchrotron radiation photoemission of core and valence levels. A physisorbed state is characterized at 80 K, whereas at 300 K an alcohoxy species is formed. White-light exposures promote a decomposition reaction which leads to carbon on the Si surface, either on elemental form or as CH(x) groups
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
Synchrotron-radiation stimulated tungsten deposition on silicon fron W(CO)6
No full textWe report a synchrotron-radiation-excited photoemission study of the adsorption of W(CO)6 on Si(111)2 x 1. W(CO)6 is shown to adsorb molecularly on Si at 100 K, and to undergo dissociation at room temperature (RT). Exposure of a reacted surface at 100 K to unmonochromatized synchrotron light results in the formation of a metal layer on Si. Such a metal layer is stable during RT annealing
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