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13.10.23: Talk by Laura Classe "Competing orders in twisted bilayer graphene"
TUM/Max-Planck Institut für Festkörperforschung Stuttgart
13.10.2023 at 15:00
Fermions in twisted bilayer graphene are described by both spin and valley degrees of freedom. Due to weak coupling between the valleys, this can lead to an approximate SU(4) symmetry made from combined rotations in spin and valley space, which plays out differently depending on filling and interactions. We show how an SU(4) symmetry emerges for itinerant fermions around charge neutrality and around Van Hove filling. We construct universal, effective models independent of details of the band structure and analyze possible patterns for spontaneous symmetry breaking for both cases. Near charge neutrality, we find instabilities towards gapped phases to be the most stable when inter channel feed-back is taken into account. We argue that other fillings away from charge neutrality are governed by Van Hove physics as observed in the pinning behavior of the Van Hove peak to the Fermi level and make use of the SU(4) symmetry to provide an explanation of the cascade of phase transitions in measurements of the density of states and of the compressibility.
Theresienstr. 37 - A 450