1,720,982 research outputs found
Cavity-mediated impact of superconductors on ferromagnetic insulators
Full text linkThis dissertation is a presentation of the research conducted during three years at the QuSpin Center for Quantum Spintronics, on the cavity-mediation of interactions between ferromagnetic insulators (FI) and superconductors (SC). We begin with a semiclassical and intuitive demonstration, followed by a comprehensive derivation of an effective, microscopic theory based on the Matsubara path integral formalism. Then, we extract the leading-order effects of the SC on the FI, namely the induction of an effective anisotropy field leading to local reorientation of the FI spins, and corrections to the FI quasiparticle spectrum. We demonstrate that the respective effects imprint the FI with information about broken inversion symmetry in the SC, and momentum anisotropy in its gap. The set-up is applicable to spintronic and superconducting circuitry, both of which are energy-efficient technologies that challenge established electronic technology.
The use of cavity-mediation distinguishes this model from proximity systems, the conventional stage for FI–SC interactions. It presents an environment in which the FI and SC can interact without the mutual disruption of their orders associated with proximity effects. Furthermore, by the application of path integrals, the cavity is integrated out exactly, leaving an exact effective FI–SC theory. Integrating out the SC, we are readily able to extract influences on the FI an order beyond mean field theory. The theory moreover takes into account the differing finite dimensions of the FI, cavity and SC, and also the separation between the FI and the SC, leaving it versatile for realistic configurations. The path integral formalism distinguished this approach from conventional theoretical frameworks for analyzing cavity-coupled systems, including classical modelling, Jaynes–Cummings-like modelling, and in particular approaches involving the Schrieffer–Wolff transformation. Unlike the latter, we are not limited analytically to off-resonant regimes.
The research has resulted in one published paper in which we present the semiclassical proof of concept that motivates the microscopic inquiry. It has also resulted in one paper ready for submission, in which the microscopic model is presented, and the anisotropy field is extracted and estimated numerically. Additionally, we present here novel, analytical expressions for the corrections to the FI quasiparticle spectrum, along with promising numerical estimates within an experimentally detectable range.
Denne avhandlingen er en sammenfatning av tre års forskning utført ved QuSpin Center for Quantum Spintronics, og omhandler kavitetsmedierte vekselvirkninger mellom ferromagnetiske isolatorer (FI) og superledere (SC). Vi begynner med en semiklassisk og intuitiv demonstrasjon, etterfulgt av en fullstendig utledning av en effektiv, mikroskopisk teori basert på Matsubaras stiintegralformalisme. Deretter trekker vi ut ledende ordens virkning av SC-en på FI-en, nemlig forårsakningen av et effektivt anisotropifelt som lokalt vender hvert av FI-ens spinn, samt av korreksjoner i spekteret til FI-ens kvasipartikler. Vi demonstrerer at de respektive virkningene etterlater avtrykk i FI-en av brutt inversjonssymmetri i SC-en, og momentumanisotropi i gapet. Oppsettet er anvendbart i spintroniske og superledende kretser, to energibesparende teknologier som utfordrer etablert elektronikk.
Bruken av kavitetsmediering skjelner vår modell fra proksimitetssystem, den konvensjonelle scenen for FI–SC-vekselvirkninger. Det legger til rette for vekselvirkninger mellom FI-en og SC-en uten den gjensidige forstyrrelsen av deres ordener tilknyttet proksimitetsvirkninger. Videre muliggjør stiintegralmetoden det å integrere ut kaviteten eksakt, som etterlater en eksakt effektiv FI–SC-teori. Etter følgelig å integrere ut SC-en, er vi lett i stand til å trekke ut virkninger på FI-en til en orden over middelfeltteori. Teorien tar dessuten høyde for de ulike, endelige størrelsene til FI-en, kaviteten og SC-en, samt separasjonen mellom FI-en og SC-en, som allsidiggjør teorien for realistiske konfigurasjoner. Stiintegralformalismen særpreger vår framgangsmåte over andre, konvensjonelle rammeverk for kavitetskoplede system, blant annet klassisk modellering, Jaynes–Cummings-lik modellering, og framgangsmåter som involverer Schrieffer–Wolff-transformasjonen. I motsetning til sistnevnte er vi ikke begrenset til ikke-resonante regimer.
Sammendrag
Forskningen har resultert i én publisert artikkel der vi legger fram det semiklassiske konseptbeviset som motiverer videre mikroskopisk oppfølging. Den har også resultert i en artikkel klar til vurdering, der den mikroskopiske teorien legges fram, sammen med et uttrykk for anisotropifeltet og et numerisk anslag av dette. I tillegg presenterer vi her nye, analytiske uttrykk for korreksjonene i spekteret til FI-ens kvasipartikler, i lag med lovende numeriske anslag i målbar orden
Proximity effects in nanostructures with geometric curvature for superconducting spintronics
No full textThis thesis explores new avenues for the field of superconducting spintronics, with a focus on hybrid structures of superconductors and geometrically curved magnetic materials. In these structures the proximity effect induces superconducting correlations in the magnetic material and we study how these correlations are influenced by geometric curvature and magnetic properties. We perform theoretical and numerical investigations to show that geometric curvature induces many interesting effects in superconducting-magnetic heterostructures, and we discuss how these effects could be exploited in new device designs for superconducting spintronics applications. Among these effects, we show that geometric curvature induces long-range supercurrents and a tunable 0-π transition in superconductor-curved ferromagnet-superconductor junctions, which means the curvature can control the direction of charge current flow. Moreover, we demonstrate how geometric curvature produces a superconducting spin-valve effect in hybrid structures of superconductors and curved ferromagnets, where the critical temperature of the system can be controlled by varying the curvature. In the context of the interplay between superconductivity and magnetism, we present a mechanism producing superconductivity in high magnetic field in multiband superconductors. Finally, we introduce a diffusive theory allowing to include geometric curvature in superconducting-antiferromagnetic heterostructures, and give a numerical analysis of observables of diffusive superconductivity in antiferromagnetic helix hybrid nanowires
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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