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Kekulé Order from Diffuse Nesting near Higher-Order Van Hove Points.

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We discovered a new mechanism called diffuse nesting that causes a sqrt[3]×sqrt[3] Kekulé density wave. This occurs due to band flattening and Fermi surface broadening near higher-order Van Hove singularities.

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Area of Science:

  • Condensed matter physics
  • Materials science
  • Theoretical physics

Background:

  • Translation symmetry-breaking order is typically suppressed by the absence of Fermi surface nesting.
  • Higher-order Van Hove singularities (HOVHS) often lack the necessary Fermi surface nesting for such orders.

Purpose of the Study:

  • To investigate the emergence of symmetry-breaking orders near HOVHS.
  • To explore a novel mechanism for Fermi surface instabilities.

Main Methods:

  • Unbiased renormalization group calculations.
  • Modeling the breathing kagome lattice.

Main Results:

  • Anisotropic band-flattening at HOVHS, combined with Fermi surface broadening, leads to approximate nesting.
  • This diffuse nesting occurs at a wave vector independent of the Fermi surface's precise shape.
  • A sqrt[3]×sqrt[3] Kekulé density wave formation is observed.

Conclusions:

  • Diffuse nesting is a new mechanism driving Fermi surface instabilities.
  • This mechanism can stabilize symmetry-breaking orders even without traditional Fermi surface nesting.
  • The findings challenge existing assumptions about the suppression of such orders near HOVHS.