Current-induced reversal of anomalous Hall conductance in twisted bilayer graphene*

Twisted bilayer graphene signatured by the flat band and strong electronic interaction at the magic angle has sparked great interests. One of the fascinating experimental observations in twisted bilayer graphene is the emergent quantum anomalous Hall effect at 3/4 filling and the sign of Hall conductance can be flipped by a dc current. The experiment implies a switching of the valley polarization and topology in twisted bilayer graphene. Here we present a theory on the current-induced switching of valley polarization and topology. The presence of current in the bulk causes the redistribution of electron occupation in bands near the Fermi energy, which then deforms and shifts the band dispersion due to the Coulomb interaction. Above a critical current, the original occupied and empty bands can be swapped resulting in the switching of valley polarization and topology in twisted bilayer graphene.