870 research outputs found

    Modulation of Kekul\'e adatom ordering due to strain in graphene

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    Intervalley scattering of carriers in graphene at `top' adatoms may give rise to a hidden Kekul\'e ordering pattern in the adatom positions. This ordering is the result of a rapid modulation in the electron-mediated interaction between adatoms at the wavevector KKK- K', which has been shown experimentally and theoretically to dominate their spatial distribution. Here we show that the adatom interaction is extremely sensitive to strain in the supporting graphene, which leads to a characteristic spatial modulation of the Kekul\'e order as a function of adatom distance. Our results suggest that the spatial distributions of adatoms could provide a way to measure the type and magnitude of strain in graphene and the associated pseudogauge field with high accuracy.Comment: 9 pages, 7 figure

    IMPACT, Fall 2016

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    https://scholarworks.sjsu.edu/impact/1014/thumbnail.jp

    Band topology and quantum spin Hall effect in bilayer graphene

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    We consider bilayer graphene in the presence of spin orbit coupling, to assess its behavior as a topological insulator. The first Chern number nn for the energy bands of single and bilayer graphene is computed and compared. It is shown that for a given valley and spin, nn in a bilayer is doubled with respect to the monolayer. This implies that bilayer graphene will have twice as many edge states as single layer graphene, which we confirm with numerical calculations and analytically in the case of an armchair terminated surface. Bilayer graphene is a weak topological insulator, whose surface spectrum is susceptible to gap opening under spin-mixing perturbations. We also assess the stability of the associated topological bulk state of bilayer graphene under various perturbations. Finally, we consider an intermediate situation in which only one of the two layers has spin orbit coupling, and find that although individual valleys have non-trivial Chern numbers, the spectrum as a whole is not gapped, so that the system is not a topological insulator.Comment: 9 pages. 9 figures include

    IMPACT, Fall 2018

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    https://scholarworks.sjsu.edu/impact/1018/thumbnail.jp

    IMPACT, Fall 2014

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    https://scholarworks.sjsu.edu/impact/1000/thumbnail.jp

    IMPACT, Fall 2012

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    https://scholarworks.sjsu.edu/impact/1004/thumbnail.jp

    IMPACT, Fall 2013

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    https://scholarworks.sjsu.edu/impact/1002/thumbnail.jp

    IMPACT, Fall 2009

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    https://scholarworks.sjsu.edu/impact/1010/thumbnail.jp

    IMPACT, Spring 2017

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    https://scholarworks.sjsu.edu/impact/1015/thumbnail.jp

    IMPACT, Spring 2011

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    https://scholarworks.sjsu.edu/impact/1007/thumbnail.jp
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