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arXiv · 1804.10009

Chiral SDW and d + id superconductivity in the magic-angle twisted bilayer-graphene

Cheng-Cheng Liu·Li-Da Zhang·Wei-Qiang Chen·Fan Yang
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Abstract

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, base on which we identify the two phases as weak-coupling FS instabilities. Then, with repulsive Hubbard interactions turning on, we performed random-phase-approximation (RPA) 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 (SDW) ordered state, featuring quantum anomalous Hall effect. The phase-diagram obtained in our approach is qualitatively consistent with experiments.

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Cheng-Cheng Liu, Li-Da Zhang, Wei-Qiang Chen, Fan Yang. 2018-11-22. Chiral SDW and d + id superconductivity in the magic-angle twisted bilayer-graphene. https://doi.org/10.1103/physrevlett.121.217001

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