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  • 1
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    High-resolution tunnelling spectroscopy of a graphene quartet (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-09-11
    Description: Electrons in a single sheet of graphene behave quite differently from those in traditional two-dimensional electron systems. Like massless relativistic particles, they have linear dispersion and chiral eigenstates. Furthermore, two sets of electrons centred at different points in reciprocal space ('valleys') have this dispersion, giving rise to valley degeneracy. The symmetry between valleys, together with spin symmetry, leads to a fourfold quartet degeneracy of the Landau levels, observed as peaks in the density of states produced by an applied magnetic field. Recent electron transport measurements have observed the lifting of the fourfold degeneracy in very large applied magnetic fields, separating the quartet into integer and, more recently, fractional levels. The exact nature of the broken-symmetry states that form within the Landau levels and lift these degeneracies is unclear at present and is a topic of intense theoretical debate. Here we study the detailed features of the four quantum states that make up a degenerate graphene Landau level. We use high-resolution scanning tunnelling spectroscopy at temperatures as low as 10 mK in an applied magnetic field to study the top layer of multilayer epitaxial graphene. When the Fermi level lies inside the fourfold Landau manifold, significant electron correlation effects result in an enhanced valley splitting for even filling factors, and an enhanced electron spin splitting for odd filling factors. Most unexpectedly, we observe states with Landau level filling factors of 7/2, 9/2 and 11/2, suggestive of new many-body states in graphene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Song, Young Jae -- Otte, Alexander F -- Kuk, Young -- Hu, Yike -- Torrance, David B -- First, Phillip N -- de Heer, Walt A -- Min, Hongki -- Adam, Shaffique -- Stiles, Mark D -- MacDonald, Allan H -- Stroscio, Joseph A -- England -- Nature. 2010 Sep 9;467(7312):185-9. doi: 10.1038/nature09330.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Nanoscale Science and Technology, NIST, Gaithersburg, Maryland 20899, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20829790" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Exceptional ballistic transport in epitaxial graphene nanoribbons (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-02-07
    Description: Graphene nanoribbons will be essential components in future graphene nanoelectronics. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length--the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also--because they can be readily produced in thousands--in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Baringhaus, Jens -- Ruan, Ming -- Edler, Frederik -- Tejeda, Antonio -- Sicot, Muriel -- Taleb-Ibrahimi, Amina -- Li, An-Ping -- Jiang, Zhigang -- Conrad, Edward H -- Berger, Claire -- Tegenkamp, Christoph -- de Heer, Walt A -- England -- Nature. 2014 Feb 20;506(7488):349-54. doi: 10.1038/nature12952. Epub 2014 Feb 5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Institut fur Festkorperphysik, Leibniz Universitat, Hannover, Appelstrasse 2, 30167 Hannover, Germany [2]. ; 1] School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA [2]. ; Institut fur Festkorperphysik, Leibniz Universitat, Hannover, Appelstrasse 2, 30167 Hannover, Germany. ; 1] Universite de Lorraine, UMR CNRS 7198, Institut Jean Lamour, BP 70239, 54506 Vandoeuvre-les-Nancy, France [2] UR1 CNRS/Synchrotron SOLEIL, Saint-Aubin, 91192 Gif sur Yvette, France. ; Universite de Lorraine, UMR CNRS 7198, Institut Jean Lamour, BP 70239, 54506 Vandoeuvre-les-Nancy, France. ; UR1 CNRS/Synchrotron SOLEIL, Saint-Aubin, 91192 Gif sur Yvette, France. ; Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Tennessee 37831, USA. ; School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA. ; 1] School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA [2] Institut Neel, CNRS UJF-INP, 38042 Cedex 6, Grenoble, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24499819" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Natural speech reveals the semantic maps that tile human cerebral cortex (2016)
    Nature Publishing Group (NPG)
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    Publication Date: 2016-04-29
    Description: The meaning of language is represented in regions of the cerebral cortex collectively known as the 'semantic system'. However, little of the semantic system has been mapped comprehensively, and the semantic selectivity of most regions is unknown. Here we systematically map semantic selectivity across the cortex using voxel-wise modelling of functional MRI (fMRI) data collected while subjects listened to hours of narrative stories. We show that the semantic system is organized into intricate patterns that seem to be consistent across individuals. We then use a novel generative model to create a detailed semantic atlas. Our results suggest that most areas within the semantic system represent information about specific semantic domains, or groups of related concepts, and our atlas shows which domains are represented in each area. This study demonstrates that data-driven methods--commonplace in studies of human neuroanatomy and functional connectivity--provide a powerful and efficient means for mapping functional representations in the brain.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852309/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852309/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Huth, Alexander G -- de Heer, Wendy A -- Griffiths, Thomas L -- Theunissen, Frederic E -- Gallant, Jack L -- EY019684/EY/NEI NIH HHS/ -- R01 EY019684/EY/NEI NIH HHS/ -- England -- Nature. 2016 Apr 28;532(7600):453-8. doi: 10.1038/nature17637.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, USA. ; Department of Psychology, University of California, Berkeley, California 94720, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27121839" target="_blank"〉PubMed〈/a〉
    Keywords: Adult ; Auditory Perception ; *Brain Mapping ; Cerebral Cortex/*anatomy & histology/*physiology ; Female ; Humans ; Magnetic Resonance Imaging ; Male ; Narration ; Principal Component Analysis ; Reproducibility of Results ; *Semantics ; *Speech
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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