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Persistent currents in a graphene ring with armchair edges.

Bor-Luen Huang1, Ming-Che Chang, Chung-Yu Mou

  • 1Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan. borluen.huang@gmail.com

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|May 24, 2012
PubMed
Summary

Graphene ribbons in the quantum spin Hall state exhibit helical edge states. Studies show edge spin currents are robust in broad ribbons but diminish in narrow ones due to coupling, and vanish with strong Rashba coupling.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Nanotechnology

Background:

  • Graphene nanoribbons with armchair edges typically lack edge states.
  • The quantum spin Hall (QSH) state necessitates the presence of helical edge states.
  • Understanding edge state behavior is crucial for topological electronic devices.

Purpose of the Study:

  • To investigate persistent charge and spin currents in graphene nanoribbons configured as rings.
  • To explore the influence of ribbon width, magnetic flux, and Rashba coupling on edge currents.
  • To determine the conditions under which a graphene nanoribbon transitions out of the QSH insulating state.

Main Methods:

  • Theoretical modeling using the tight-binding approximation.
  • Simulation of graphene ribbons folded into rings subjected to magnetic flux.
  • Analysis of persistent charge and spin currents as a function of ribbon geometry and coupling strengths.

Main Results:

  • Broad graphene ribbons in the QSH state exhibit a robust, radius-independent edge spin current.
  • Inter-edge coupling in narrow ribbons can open the Dirac gap, reducing persistent currents.
  • Increasing Rashba coupling leads to a decrease in persistent spin current, vanishing at a critical value.

Conclusions:

  • The study reveals distinct behaviors of edge currents in graphene nanoribbons based on their width and coupling.
  • A critical Rashba coupling strength signifies the loss of the quantum spin Hall insulating phase.
  • These findings have implications for the design of spintronic and topological electronic devices.