138 research outputs found

    Quantum dot behavior in graphene nanoconstrictions

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    Graphene nanoribbons display an imperfectly understood transport gap. We measure transport through nanoribbon devices of several lengths. In nanoribbons of length greater than or equal to 250 nm we observe transport through multiple quantum dots in series, while shorter constrictions of length less than or equal to 60 nm display behavior characteristic of single and double quantum dots. Dot size scales with constriction width. We propose a model where transport occurs through quantum dots that are nucleated by background disorder potentials in the presence of a confinement gap.Comment: published version: 24 pages, 9 figures (includes supplementary information

    Kondo effect and spin filtering in triangular artificial atoms

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    We study strongly correlated states in triangular artificial atoms. Symmetry-driven orbital degeneracy of the single particle states can give rise to an SU(4) Kondo state with entangled orbital and spin degrees of freedom, and a characteristic phase shift δ=π/4\delta = \pi/4. Upon application of a Zeeman field, a purely orbital Kondo state is formed with somewhat smaller Kondo temperature and a fully polarized current through the device. The Kondo temperatures are in the measurable range. The triangular atom also provides a tool to systematically study the singlet-triplet transitions observed in recent experiments.Comment: 5 pages, 2 figure
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