127 research outputs found
Surface superconductivity in multilayered rhombohedral graphene: Supercurrent
The supercurrent for the surface superconductivity of a flat-band
multilayered rhombohedral graphene is calculated. Despite the absence of
dispersion of the excitation spectrum, the supercurrent is finite. The critical
current is proportional to the zero-temperature superconducting gap, i.e., to
the superconducting critical temperature and to the size of the flat band in
the momentum space
Tailoring the thermal Casimir force with graphene
The Casimir interaction is omnipresent source of forces at small separations between bodies, which is difficult to change by varying external conditions. Here we show that graphene interacting with a metal can have the best known force contrast to the temperature and the Fermi level variations. In the distance range 50–300 nm the force is measurable and can vary a few times for graphene with a bandgap much larger than the temperature. In this distance range the main part of the force is due to the thermal fluctuations. We discuss also graphene on a dielectric membrane as a technologically robust configuration
Electron-Phonon Coupling in Highly-Screened Graphene
Photoemission studies of graphene have resulted in a long-standing
controversy concerning the strength of the experimental electron-phonon
interaction in comparison with theoretical calculations. Using high-resolution
angle-resolved photoemission spectroscopy we study graphene grown on a copper
substrate, where the metallic screening of the substrate substantially reduces
the electron-electron interaction, simplifying the comparison of the
electron-phonon interaction between theory and experiment. By taking the
nonlinear bare bandstructure into account, we are able to show that the
strength of the electron-phonon interaction does indeed agree with theoretical
calculations. In addition, we observe a significant bandgap at the Dirac point
of graphene.Comment: Submitted to Phys. Rev. Lett. on July 20, 201
Factor Analysis and the Social Capital Index: A Study at the Brazil / Bolivia Border
Objective: The study aimed to build the level of social capital by neighborhoods Guajará-Mirim border region between the State of Rondônia, Brazil and the Republic of Bolivia, which in recent years has been showing signs of social fragility due advance not virtuous practices. Method: This work made use of research in secondary bases as well as in primary bases. The tabulation of qualitative and quantitative data was performed in Excel (2010) and for their processing performance index construction purposes were calculated following the factorial analysis techniques presented by Hair et al. [19] Santana [20, 21]; and Choi [22]. For this, we made use of the statistical tool SPSS (Statistical Package for Social Sciences) for the construction of the indices of social capital. The correlation analysis process was done in Excel. results: It was observed that the capital reached regular levels in Guajará-Mirim neighborhoods not observable, so correlations between the studied parameters, however, it needs to be further studied as factors such as the flooding of the Mamore river may have interfered in any way in the implementation process of the field survey to the residents of the city. It became clear that the municipality of Guajará-Mirim suffers from serious social problems and that most problems are correlated with the increase in alcoholic beverage market in the city and use drugs. However, was not observed as the institutional arrangements are dealing with this problem, that is, as public bodies are relating to discuss actions for concrete solutions to this evil that plagues large portion of the population of Guajará-Mirim, mainly young teenagers residents of Guajá-Mamim. However, we hope to continue this work in order to better understand this mechanism of social network between the actors of this process in the region
Local Power as the Basis of the Understanding of the Federative Pact
The research aimed to describe the existing problems in the relationship between City, State and Federal Government, through the Brazilian Federative Pact, mainly for municipalities with population of less than 50,000 inhabitants. The research is structured from a qualitative perspective. The theoretical framework was built from the local power of the discussion based on the understanding of the federal pact and local interest and the municipality in Brazil. The paper argues that the federal pact is little debated, discussed, much less questioned by society in general, it only strengthens the lack of a legal and institutional framework for coordination and cooperation among federal entities in the country, which results in public policy fragmented the territory and without direction, causing waste of public resources
The Physics of Kondo Impurities in Graphene
This article summarizes our understanding of the Kondo effect in graphene,
primarily from a theoretical perspective. We shall describe different ways to
create magnetic moments in graphene, either by adatom deposition or via
defects. For dilute moments, the theoretical description is in terms of
effective Anderson or Kondo impurity models coupled to graphene's Dirac
electrons. We shall discuss in detail the physics of these models, including
their quantum phase transitions and the effect of carrier doping, and confront
this with existing experimental data. Finally, we point out connections to
other quantum impurity problems, e.g., in unconventional superconductors,
topological insulators, and quantum spin liquids.Comment: 27 pages, 8 figs. Review article prepared for Rep. Prog. Phys. ("key
issues" section). (v2) Final version as publishe
Effect of Coulomb interactions on the physical observables of graphene
We give an update of the situation concerning the effect of electron-electron
interactions on the physics of a neutral graphene system at low energies. We
revise old renormalization group results and the use of 1/N expansion to
address questions of the possible opening of a low-energy gap, and the
magnitude of the graphene fine structure constant. We emphasize the role of
Fermi velocity as the only free parameter determining the transport and
electronic properties of the graphene system and revise its renormalization by
Coulomb interactions in the light of recent experimental evidence.Comment: Proceedings of the Nobel Symposium on graphene 2010, to appear as a
special issue in Physica Script
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