Winding Vector: How to Annihilate Two Dirac Points with the Same Charge.

@article{Montambaux2018WindingVH,
  title={Winding Vector: How to Annihilate Two Dirac Points with the Same Charge.},
  author={G. Montambaux and Lih-King Lim and J N Fuchs and Fr{\'e}d{\'e}ric Pi{\'e}chon},
  journal={Physical review letters},
  year={2018},
  volume={121 25},
  pages={
          256402
        }
}
The merging or emergence of a pair of Dirac points may be classified according to whether the winding numbers which characterize them are opposite (+- scenario) or identical (++ scenario). From the touching point between two parabolic bands (one of them can be flat), two Dirac points with the same winding number emerge under appropriate distortion (interaction, etc.), following the ++ scenario. Under further distortion, these Dirac points merge following the +- scenario, that is corresponding… 
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