TY - JOUR

T1 - Phase diagram of twisted bilayer graphene at filling factor ν=±3

AU - Xie, Fang

AU - Kang, Jian

AU - Bernevig, B. Andrei

AU - Vafek, Oskar

AU - Regnault, Nicolas

N1 - Publisher Copyright:
© 2023 American Physical Society.

PY - 2023/2/15

Y1 - 2023/2/15

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85149671843&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85149671843&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.107.075156

DO - 10.1103/PhysRevB.107.075156

M3 - Article

AN - SCOPUS:85149671843

SN - 2469-9950

VL - 107

JO - Physical Review B

JF - Physical Review B

IS - 7

M1 - 075156

ER -