1,721,006 research outputs found
Crystal growth, characterization, and point-contact Andreev-reflection spectroscopy of the noncentrosymmetric superconductor Mo 3 Al 2 C
No full textWe report on the first successful growth of single crystals of the noncentrosymmetric superconductor Mo3Al2C obtained by means of a cubic-anvil, high-pressure, and high-temperature technique. Composition, structure, and normal-state transport properties of the crystals were studied by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, magnetic susceptibility, and resistivity measurements as a function of temperature. Variations in critical temperature (Tc) between 8.6 and 9.3 K were observed, probably due to the slightly different carbon stoichiometry of the samples. Single-crystal x-ray refinement confirmed the high structural perfection of the grown crystals. Remarkably, the refined Flack parameter values for all the measured crystals using a P4132 space-group model were consistently close to either 0 or 1, hence indicating that the considered crystals belong to two enantiomorphic space groups, P4132 and P4332. An anomaly in the resistivity is observed at 130 K, most likely associated with the onset of a charge-density-wave phase. The superconducting properties (and in particular the symmetry, the amplitude, and the temperature dependence of the superconducting gap) were studied by using point contact Andreev-reflection spectroscopy. The results confirm that Mo3Al2C is a moderately strongly-coupled superconductor with 2Delta/kBTc = 4 and unambiguously prove that the order parameter has an s-wave symmetry despite the asymmetric spin-orbit coupling arising from the lack of inversion symmetry
Energy dependence of the normal density of states and of the electron-phonon spectral function in the quasiparticle tunneling of high-Tc superconductors
No full textWe discuss the effects of quasiparticle energy dependence of the normal density of states on the Eliashberg equations in the case of high-Tc superconductors and compare the numerical results with our recent tunneling experimental data in Bi2Sr2CaCu2O8+x with Tc = 93 K. We also consider the possibility of quasiparticle energy dependence of the electron-phonon spectral function α2(Ω)F(Ω) and calculate its effects on the superconducting density of states
Probing the current-phase relation in Josephson point-contact junctions between Pb 0.6 In 0.4 and Ba 0.6 K 0.4 (FeAs) 2 superconductors
Get PDFThe Josephson effect in point contacts between an “ordinary” superconductor Pb 0.6In0.4 (Tc≈6.6K) and single crystals of the Fe-based superconductor Ba0.6K0.4(FeAs)2 (Tc≈38.5K), was investigated. In order to shed light on the order parameter symmetry of Ba0.6K0.4(FeAs)2, the dependence of the Josephson supercurrent Is on the temperature and on sin (dφ) with d= 1 , 2 was studied. The dependencies of the critical current on temperature Ic(T) and of the amplitudes of the first current steps of the current–voltage characteristic inexp(P)(n= 0 , 1 , 2) on the power of microwave radiation with frequency f=(1.5÷8)GHz were measured. It is shown that the dependencies Ic(T) are close to the well-known Ambegaokar–Baratoff (AB) dependence for tunnel contacts between “ordinary” superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an “ordinary” superconductor and a two-band superconductor with s± order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies inexp(P) cannot be approximated within the resistively shunted model using the normalized microwave frequencies Ω = 2 πf/ (2 eVc/ ħ) with characteristic voltages Vc= IcRN, (RN—normal resistance of the contact) found from the low-voltage parts of the current–voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of Ω , which takes into account all the features of the point contact affecting the period of the dependence inexp(P). An analysis of the Ic(T) and inexp(P) dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the sin of the phase difference φ, Is= Icsin(φ). The implications of these results on the symmetry of the order parameter are also discussed
Eliashberg equations, pair symmetry and tunnel density of states in the optimally-doped high-Tc superconductor Bi2Sr2CaCu2O8+x
No full textIn this work, in order to compare the theoretical density of states (DOS) to the tunneling data in the optimally-doped high-Tc superconductor (HTS) Bi2Sr2CaCu2O8+x, we calculate the real-axis direct solution of the d-wave equations for the retarded electron-boson interaction in presence of half-filling and impurities. The use of a spectral function containing an isotropic part αs2F(Ω) and an anisotropic one αd2F(Ω) and the simple assumption: αd2F(Ω) = gdαs2F(Ω) where gd is a constant leads, for appropriate values of the isotropic coupling constant λs and the anisotropic one λd, to solutions with only d-wave symmetry for the order parameter Δ(ω) and only s-wave one for the renormalization function Z(ω). The results properly fit both the critical temperature and the DOS in the whole energy range, as recently determined in our break-junction tunneling experiments, but appear unable to do the same in the case of recent STM data
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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