The nature of correlations in the insulating states of twisted bilayer graphene

The recently observed superconductivity in twisted bilayer graphene emerges from insulating states believed to arise from electronic correlations. While there have been many proposals to explain the insulating behavior, the commensurability at which these states appear suggests they are Mott insulators. We focus on the insulating states with ±2 electrons or holes with respect to the charge neutrality point. We show that the theoretical expectations for the Mott insulating states are not compatible with the experimental dependences on temperature and magnetic field if, as frequently assumed, only onsite (local) correlations are included. We argue that the inclusion of intersite correlations in the treatment of the Hubbard model can bring the predictions for the magnetic and temperature dependencies of the Mott transition to an agreement with experiments. The importance of these non-local correlations indicates that the observed insulating gap is not the one between the Hubbard bands and that antiferromagnetic-like correlations play a key role in the Mott metal insulator transition. arXiv:1805.07303.