1,720,981 research outputs found
Screening of pair fluctuations in superconductors with coupled shallow and deep bands: A route to higher-temperature superconductivity
No full textA combination of strong Cooper pairing and weak superconducting fluctuations is crucial to achieve and stabilize high-Tc superconductivity. We demonstrate that a coexistence of a shallow carrier band with strong pairing and a deep band with weak pairing, together with the Josephson-like pair transfer between the bands to couple the two condensates, realizes an optimal multicomponent superconductivity regime: it preserves strong pairing to generate large gaps and a very high critical temperature but screens the detrimental superconducting fluctuations, thereby suppressing the pseudogap state. Surprisingly, we find that the screening is very efficient even when the interband coupling is very small. Thus, a multiband superconductor with a coherent mixture of condensates in the BCS regime (deep band) and in the BCS-BEC crossover regime (shallow band) offers a promising route to higher critical temperatures
Multiband Material with a Quasi-1D Band as a Robust High-Temperature Superconductor
Get PDFIt is well known that superconductivity in quasi-one-dimensional (Q1D) materials is hindered by large fluctuations of the order parameter. They reduce the critical temperature and can even destroy the superconductivity altogether. Here it is demonstrated that the situation changes dramatically when a Q1D pair condensate is coupled to a higher-dimensional stable one, as in recently discovered multiband Q1D superconductors. The fluctuations are suppressed even by vanishingly small pair-exchange coupling between different band condensates and the superconductor is well described by the mean field theory. In this case the low dimensionality effects enhance the coherence of the system instead of suppressing it. As a result, the critical temperature of the multiband Q1D superconductor can increase by orders of magnitude when the system is tuned to the Lifshitz transition with the Fermi level close to the edge of the Q1D band
Suppression of fluctuations in a two-band superconductor with a quasi-1D band
No full textChain-like structured superconductive materials (such as A_2Cr_3As_3, with A
= K, Rb, Cs) exhibit the multiband electronic structure of single-particle
states, where coexisting quasi-one-dimensional (Q1D) and conventional
higher-dimensional energy bands take part in the creation of the aggregate
superconducting condensate. When the chemical potential approaches the edge of
a Q1D band in a single-band superconductor, the corresponding mean-field
critical temperature increases significantly but the superconductivity is
quenched by fluctuations. However, recent investigation has revealed that when
a Q1D band is coupled to a higher dimensional one by the interband Cooper-pair
transfer, the thermal superconductive fluctuations can be suppressed so that
the resulting critical temperature can be close to its mean-field value. In the
present work, we calculate the mean-field T_c0 and fluctuation-shifted T_c
critical temperatures for a two-band superconductor where a Q1D band coexists
with a higher-dimensional band, and investigate how the thermal fluctuations
are sensitive to the system parameters. We find that T_c is close to T_c0 in a
wide range of microscopic parameters, and even the dimensionality of the
higher-dimensional band does not play an essential role. Thus, the screening
mechanism for suppressing fluctuations via the pair-exchange coupling between
the bands is indeed relevant for a large class of Q1D multiband superconducting
materials, encouraging further experiments aimed at reaching larger critical
temperatures in such multiband superconductors.Comment: 11 pages, 5 figures, and Appendix with the calculations of the
Ginzburg-Landau coefficients for a quasi-one-dimensional ban
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
Crossband versus intraband pairing in superconductors: signatures and consequences of the interplay
Get PDFAbstract: We analyze the paradigmatic competition between intraband and crossband Cooper-pair formation in twoband superconductors, neglected in most works to date. We derive the phase-sensitive gap equations and describe the crossover between the intraband-dominated and the crossband-dominated regimes, delimited by a "gapless" state. Experimental signatures of crosspairing comprise notable gap splitting in the excitation spectrum, non-BCS behavior of gaps versus temperature, as well as changes in the pairing symmetry as a function of temperature. The consequences of these findings are illustrated on the examples of MgB2 and Ba0.6K0.4Fe2As2
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
BCS-BEC crossover induced by a shallow band: Pushing standard superconductivity types apart
No full textThe appearance of a shallow band(s) drives a superconductor towards the BCS-BEC crossover, conventionally
associated with notable changes in single-particle properties and an elevated critical temperature. Here we
demonstrate that the proximity to the crossover induced by a shallow band has also a dramatic effect on the phase
diagram of the superconducting magnetic properties. When the system passes from the BCS to BEC regime, the
intertype domain between superconductivity types I and II enlarges systematically, being inversely proportional
to the square of the Cooper-pair radius, the main parameter that controls the BCS-BEC superconductivity. We
also show that despite the presence of a shallow band, the condensate fluctuations are suppressed when it coexists
in one material with standard deep bands, as in recent iron chalcogenides FeSe x Te 1−x and FeSe
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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