Phase diagram of twisted bilayer graphene at filling factor ν=±3

Fang Xie, Jian Kang, B. Andrei Bernevig, Oskar Vafek, Nicolas Regnault

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Abstract

We study the correlated insulating phases of twisted bilayer graphene (TBG) in the absence of lattice strain at integer filling ν=±3. Using the self-consistent Hartree-Fock method on a particle-hole symmetric model and allowing translation symmetry breaking terms, we obtain the phase diagram with respect to the ratio of AA interlayer hopping (w0) and AB interlayer hopping (w1). When the interlayer hopping ratio is close to the chiral limit (w0/w10.5), a quantum anomalous Hall state with Chern number νc=±1 can be observed consistent with previous studies. Around the realistic value w0/w1≈0.8, we find a spin and valley polarized, translation symmetry breaking, state with C2zT symmetry, a charge gap and a doubling of the moiré unit cell, dubbed the C2zT stripe phase. The real-space total charge distribution of this C2zT stripe phase in the flat band limit does not have modulation between different moiré unit cells, although the charge density in each layer is modulated, and the translation symmetry is strongly broken. Other symmetries, including C2z, C2x, particle-hole symmetry P, and the topology of the C2zT stripe phase, are also discussed in detail. We observed braiding and annihilation of the Dirac nodes by continuously turning on the order parameter to its fully self-consistent value, and provide a detailed explanation of the mechanism for the charge gap opening despite preserving C2zT and valley U(1) symmetries. In the transition region between the quantum anomalous Hall phase and the C2zT stripe phase, we find an additional competing state with comparable energy corresponding to a phase with a tripling of the moiré unit cell.

Original languageEnglish (US)
Article number075156
JournalPhysical Review B
Volume107
Issue number7
DOIs
StatePublished - Feb 15 2023

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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