Chiral SDW and d + id superconductivity in the magic-angle twisted bilayer-graphene
Abstract
We model the newly synthesized magic-angle twisted bilayer-graphene superconductor with two -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 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.
Keywords
Cite
@article{arxiv.1804.10009,
title = {Chiral SDW and d + id superconductivity in the magic-angle twisted bilayer-graphene},
author = {Cheng-Cheng Liu and Li-Da Zhang and Wei-Qiang Chen and Fan Yang},
journal= {arXiv preprint arXiv:1804.10009},
year = {2018}
}
Comments
First submitted to PRL in April 26th, accepted in October 22nd. Here we for the first time proposed that the pairing mechanism in this system is "exchanging density-wave fluctuation". We also for the first time related the emergence of the "correlated insulator" and SC in this material to the presence of the van-Hove singularity and the FS-nesting within the flat band