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Transport through the AIAs barrier involving states associated with X point
No full textLink archiwalny https://depotuw.ceon.pl/handle/item/361
Transport through the AIAs barrier involving states associated with X point
No full textCelem pracy było opracowanie modelu opisujacego tunelowanie przez struktury
warstwowe. Model ten opiera sie na nierównowagowych funkcjach Greena w
przyblizeniu ciasnego wiazania. Rozwazane sa przejscia w których zachowana
jest prostopadła do kierunku wzrostu struktury składowa pedu i dla takich
przejsc opisane zostały dwa mechanizmy tunelowania – przez stany zwiazane
z punktem X lezacym na osi układu oraz przez stany zwiazane z bocznymi
punktami X.
Obliczenia numeryczne wykonane zostały dla struktury GaAs/AlAs/GaAs w
dwóch kierunkach [001] i [111]. Uwzgledniono takze obecnosc warstwy domieszkowej.
Widoczne na wykresach charakterystyk pradowo napieciowych struktury
schodkowe, za pomoca analizy gestosci spektralnej zostały powiazane z
otwieraniem sie kolejnych kanałów transportu.The model describing the tunneling through quantum barrier in semiconductor
layered structures was developed. The model was based on nonequilibrium
Green functions in tight binding approach. Tunneling of carriers conserving
pseudomomentum in the plane of the layers (x-y plane) was considered. For
such transitions two mechanisms of tunneling were described: a). tunneling
through the X point states at the direction of tunneling ( Xz states) , b).
tunneling through the side X points ( Xxy states).
Numerical calculations were performed for GaAs/AlAs/GaAs structure for two
directions of tunneling: [001] and [111]. The presence of doping layer was taken
into account. The resulting current-voltage plotscharacteristics revealed steplike
structures, which were analyzed by spectral density method and were
related to opening of subsequent channels of transport
Realizing optical persistent spin helix and stern-gerlach deflection in an anisotropic liquid crystal microcavity
No full textSpin-orbit interactions which couple the spin of a particle with its momentum degrees of freedom lie at the center of spintronic applications. Of special interest in semiconductor physics are Rashba and Dresselhaus spin-orbit coupling. When equal in strength, the Rashba and Dresselhaus fields result in SU(2) spin rotation symmetry and emergence of the persistent spin helix only investigated for charge carriers in semiconductor quantum wells. Recently, a synthetic Rashba-Dresselhaus Hamiltonian was shown to describe cavity photons confined in a microcavity filled with optically anisotropic liquid crystal. In this Letter, we present a purely optical realization of two types of spin patterns corresponding to the persistent spin helix and the Stern-Gerlach experiment in such a cavity. We show how the symmetry of the Hamiltonian results in spatial oscillations of the spin orientation of photons traveling in the plane of the cavity
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
A New Approach to the Theory of Photoemission from Solids
No full textBy neglecting certain terms in the Hamiltonian (of importance only in the immediate neighbourhood of the threshold energy) we are able to write an exact expression for the photoemission intensity which involves the standard time inverted LEED state and broadened hole-states. If inelastic extrinsic losses are neglected our expression is similar to the one used by e.g. Feibelman and Eastman [1], Pendry [2] and Spanjaard et al. [3]. Our theory also allows inelastic losses (including interference between intrinsic and extrinsic losses) to be evaluated. The expressions are similar to those obtained by Inglesfield [4], but the damping effect no longer has to be put in by hand. Our theory further can handle not only core electron but also valence electron photoemission and it is not restricted to metals but applies to all types of solids. We have also traced why and when Inglesfield's one step theory agrees with a semiclassical calculation
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
Topological phase transition and evolution of edge states in In-rich InGaN/GaN quantum wells under hydrostatic pressure
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