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Exact and perturbative insulator states and excitations in twisted bilayer graphene

ORAL

Abstract

We study the low energy states of the flat-band projected Hamiltonian of magic angle twisted bilayer graphene with Coulomb interactions. By treating the nonchiral interaction and the kinetic energy as perturbations, we analytically derive the exact or perturbative strongly interacting (Chern) insulator ground states at all integer fillings |\nu|<4. We find the ground state has Chern number mod(\nu,2), and is intervalley coherent (valley polarized) at fillings |\nu|=0,1,2 (|\nu|=3). We further show that the insulators have analytically computable charge 0, +-1,+-2 excitations. We show that the Goldstone modes of the ground states are quadratic. Furthermore, from the charge 1 and 2 excitations, we prove the absence of Cooper pairing from the Coulomb interaction in the flat band limit, which suggests other superconductivity mechanisms.

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Presenters

  • Biao Lian

    Princeton University, Princeton Center for Theoretical Science, Princeton University, Physics, Princeton University

Authors

  • Biao Lian

    Princeton University, Princeton Center for Theoretical Science, Princeton University, Physics, Princeton University

  • Zhida Song

    Princeton University

  • Nicolas Regnault

    Department of Physics, Princeton University, Princeton University, Ecole Normale Superieure, Physics, Princeton University

  • Aditya Cowsik

    Stanford University, Physics, Princeton University

  • Fang Xie

    Princeton University, Physics, Princeton University

  • Dmitri K. Efetov

    ICFO-The Institute of Photonic Sciences, ICFO, ICFO – The Institute of Photonic Sciences

  • Ali Yazdani

    Princeton University, Joseph Henry Laboratories & Department of Physics, Princeton University

  • Andrei B Bernevig

    Department of Physics, Princeton University, Princeton University, Princeto University, Princeton, USA, Physics, Princeton University