1,720,981 research outputs found
Percolation transitions in bilayer graphene encapsulated by hexagonal boron nitride
No full textWe studied the plateau-plateau transitions that characterize the electrical transport in the quantum Hall regime
in a high mobility bilayer graphene flake encapsulated by hexagonal boron nitride at magnetic fields up to 9 T and
temperatures above 300 mK. We measured independently the exponent κ of the temperature-induced transition
broadening, the critical exponent γ of the localization length, and the exponent p ruling the temperature scaling of
the coherence length, finding consistencywith the relation γ = p/2κ. The observed value of κ = 0.30(0.28,0.32)
deviates from that of the quantum Hall critical point. The obtained γ = 1.25(0.96,1.54) questions the validity of
a pure Anderson transition, and reveals percolation as the underlying driving mechanism
Quantum interference corrections to magnetoconductivity in graphene
No full textWe studied weak localization (WL) and antilocalization (WAL) in graphene at temperatures between 0.3 K and
15 K. At low carrier density, we observed a transition fromWL toWAL driven by the increasing of the magnetic
field while at high carrier density, WAL was suppressed as a consequence of trigonal warping of the conical
energy bands.We analyzed the magnetic-field-driven WL-WAL transition, evaluating the relative strengths of the
various elastic-scattering mechanisms and estimating the decoherence lengths and rates as a function of
temperature, using an alternative method with respect to previously reported studies. We relate the small values
of lφ here reported, confirmed by a complementary analysis of universal conductance fluctuations, to an effective
breaking of time-reversal symmetry due to the slowly varying disorder of the long-range type
Disorder and de-coherence in graphene probed by low-temperature magneto-transport: weak localization and weak antilocalization
No full textWe studied weak localization (WL) and and weak antilocalization (WAL) in a eight-contacts Hall bar made of exfoliated monolayer graphene on Si-SiO2, by means of magneto-transport experiments, at temperatures between 0.3 K and 15 K. At low carrier density (n ≊ 7 × 1011 cm−2) we observed a transition from WL to WAL driven by the increasing of the magnetic field, while at high carrier density (n ≊ 2 × 1012 cm−2) only WL was observable. We analyzed the magnetic field driven WL-WAL transition and we evaluated the temperature dependence of the de-coherence parameters using an alternative method compared to previous studies. The values we obtained were corroborated by a root-mean-square analysis of the amplitude of highly-reproducible universal conductance fluctuations
Temperature- and density-dependent transport regimes in a h-BN/bilayer graphene/h-BN heterostructure
No full textWe report on multiterminal electrical transport measurements performed on a bilayer graphene sheet enclosed by two hexagonal boron nitride flakes. We characterize the temperature dependence of electrical resistivity from 300 mK to 50 K, varying the carrier densities with a back gate. The resistivity curves clearly show a temperature-independent crossing point at density n=nc≈2.5×1011 cm−2 for both positive and negative carriers, separating two distinct regions with dρ/dT0, respectively. Our analysis rules out the possibility of a zero-T quantum phase transition, revealing instead the onset of robust ballistic transport for n>nc, while the T dependence close to the neutrality point is the one expected from the parabolic energy-momentum relation. At low temperature (T≪10 K), the data are compatible with transport via variable range hopping mediated by localized impurity sites, with a characteristic exponent 1/3 that is renormalized to 1/2 by Coulomb interaction in the high-density regime
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
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