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

ORAL

Abstract

We model the newly synthesized magic-angle twisted bilayer-graphene superconductor with two px,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 experimental observations. Van-Hove singularity and Fermi-surface 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.


Reference: Cheng-Cheng Liu, Li-Da Zhang, Wei-Qiang Chen, and Fan Yang, arXiv:1804.10009 (2018). (Accepted by PRL)

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Presenters

  • Cheng-Cheng Liu

    Beijing Key Laboratory of Nanophotonics and Ultrane Optoelectronic Systems, School of Physics, Beijing Institute of Technology, School of Physics, Beijing Institute of Technology, Beijing, China, School of Physics, Beijing Institute of Technology

Authors

  • Cheng-Cheng Liu

    Beijing Key Laboratory of Nanophotonics and Ultrane Optoelectronic Systems, School of Physics, Beijing Institute of Technology, School of Physics, Beijing Institute of Technology, Beijing, China, School of Physics, Beijing Institute of Technology

  • Li-Da Zhang

    School of Physics, Beijing Institute of Technology, Beijing, China, Beijing Institute of Technology

  • Wei-Qiang Chen

    Department of Physics, Southern University of Science and Technology, Shenzhen, China

  • Fan Yang

    School of Physics, Beijing Institute of Technology, School of Physics, Beijing Institute of Technology, Beijing, China, Beijing Institute of Technology