title: Interaction-Induced Dirac Fermions from Quadratic Band Touching in Bilayer Graphene.
abstract: We revisit the effect of local interactions on the quadratic band touching (QBT) of the Bernal honeycomb bilayer model using renormalization group (RG) arguments and quantum Monte Carlo (QMC) simulations. We present a RG argument which predicts, contrary to previous studies, that weak interactions do not flow to strong coupling even if the free dispersion has a QBT. Instead, they generate a linear term in the dispersion, which causes the interactions to flow back to weak coupling. Consistent with this RG scenario, in unbiased QMC simulations of the Hubbard model we find compelling evidence that antiferromagnetism turns on at a finite U/t despite the U=0 hopping problem having a QBT. The onset of antiferromagnetism takes place at a continuous transition which is consistent with (2+1)D Gross-Neveu criticality. We conclude that generically in models of bilayer graphene, even if the free dispersion has a QBT, small local interactions generate a Dirac phase with no symmetry breaking and that there is a finite-coupling transition out of this phase to a symmetry-broken state.
authors: Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors: Sumiran
authors: S
authors: Pujari
authors: Institute for Theoretical Physics, University of Innsbruck, 6020 Innsbruck, Austria.
authors: Thomas C
authors: TC
authors: Lang
authors: Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors: Ganpathy
authors: G
authors: Murthy
authors: Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors: Ribhu K
authors: RK
authors: Kaul