Bilayer graphene band structure showing that the conduction and valence bands touch each other at the corners of the hexagonal Brillouin zone.

From the article:

Anomalous Sequence of Quantum Hall Liquids Revealing a Tunable Lifshitz Transition in Bilayer Graphene
Anastasia Varlet, Dominik Bischoff, Pauline Simonet, Kenji Watanabe, Takashi Taniguchi, Thomas Ihn, Klaus Ensslin, Marcin Mucha-Kruczyński, and Vladimir I. Fal’ko
Phys. Rev. Lett. 113, 116602 (2014)

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