Chiral Spin Density Wave and d+id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene

We model the newly synthesized magic-angle-twisted bilayer graphene superconductor with two p_{x,y}-like Wannier orbitals on the superstructure honeycomb lattice, where the hopping integrals are constructed via the Slater-Koster formulism by symmetry analysis. The characteristics exhibited in this s...

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Bibliographic Details
Published in:Physical review letters 2018-11, Vol.121 (21), p.217001-217001
Main Authors: Liu, Cheng-Cheng, Zhang, Li-Da, Chen, Wei-Qiang, Yang, Fan
Format: Article
Language:English
Subjects:
Bilayers
Graphene
Honeycomb construction
Mathematical models
Nesting
Phase diagrams
Quantum Hall effect
Spin density waves
Superstructures
Unconventional superconductivity
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Summary:We model the newly synthesized magic-angle-twisted bilayer graphene superconductor with two p_{x,y}-like Wannier orbitals on the superstructure honeycomb lattice, where the hopping integrals are constructed via the Slater-Koster formulism by symmetry analysis. The characteristics exhibited in this simple model are well consistent with both the rigorous calculations and experiment observations. A van Hove singularity and Fermi-surface (FS) nesting are found in the doping levels relevant to the correlated insulator and unconventional superconductivity revealed experimentally, based on which we identify the two phases as weak-coupling FS instabilities. Then, with repulsive Hubbard interactions turned on, we performed random-phase-approximation based calculations to identify the electron instabilities. As a result, we find chiral d+id topological superconductivity bordering the correlated insulating state near half-filling, identified as noncoplanar chiral spin-density wave ordered state, featuring the quantum anomalous Hall effect. The phase diagram obtained in our approach is qualitatively consistent with experiments.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.121.217001