Isospin- and momentum-polarized orders in bilayer graphene

Electron bands in Bernal bilayer graphene flatten out in a transverse electric field, offering a promising platform for correlated electron physics. We discuss the spin/valley isospin magnetism resembling that seen in moire bands. We predict that the isospin magnetism coexists with momentum-polarized phases occurring via a flocking transition in momentum space in which the electron distribution is spontaneously displaced in momentum space relative to the K and K' valley centers. The momentum-polarized phases feature electronic nematicity manifest in the anisotropy of transport, and unusual observables such as persistent currents in the ground state. Momentum-polarized carriers sample the Berry curvature of the conduction band, resulting in a longitudinal and anomalous Hall conductivity that displays switching upon the flocking transition and other effects that do not occur in previously studied systems.

Automated summary

Electron bands in Bernal bilayer graphene become flat in a transverse electric field, providing a promising platform for studying correlated electron physics. Similar to the moire bands, we discuss the spin/valley isospin magnetism observed in this system. We predict that the isospin magnetism coexists with momentum-polarized phases and exhibits distinct phenomena such as spontaneous displacement in momentum space and electronic nematicity, resulting in anisotropy in transport and persistent currents in the ground state. Furthermore, momentum-polarized carriers sample the Berry curvature, leading to unique behavior such as switching of longitudinal and anomalous Hall conductivity during the flocking transition.