Ferromagnetism in Narrow Bands of Moiré Superlattices
Name
PhysRevLett.124.187601.pdf
Description
Published version
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297.01 KB
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Adobe PDF
Checksum (MD5)
3bb5413d1f54574f6a958a16548affab
Author(s)
Repellin, Cécile
Dong, Zhihuan
Zhang, Ya-Hui
Senthil, T
Date Issued
2020
Journal
Physical Review Letters
Publisher
American Physical Society (APS)
Citation
Repellin, Cécile, Dong, Zhihuan, Zhang, Ya-Hui and Senthil, T. 2020. "Ferromagnetism in Narrow Bands of Moiré Superlattices." Physical Review Letters, 124 (18).
Version
Final published version
Abstract
© 2020 American Physical Society. Many graphene moiré superlattices host narrow bands with nonzero valley Chern numbers. We provide analytical and numerical evidence for a robust spin and/or valley polarized insulator at total integer band filling in nearly flat bands of several different moiré materials. In the limit of a perfectly flat band, we present analytical arguments in favor of the ferromagnetic state substantiated by numerical calculations. Further, we numerically evaluate its stability for a finite bandwidth. We provide exact diagonalization results for models appropriate for ABC trilayer graphene aligned with hBN, twisted double bilayer graphene, and twisted bilayer graphene aligned with hBN. We also provide DMRG results for a honeycomb lattice with a quasiflat band and nonzero Chern number, which extend our results to larger system sizes. We find a maximally spin and valley polarized insulator at all integer fillings when the band is sufficiently flat. We also show that interactions may induce effective dispersive terms strong enough to destabilize this state. These results still hold in the case of zero valley Chern number (for example, trivial side of TLG/hBN). We give an intuitive picture based on extended Wannier orbitals, and emphasize the role of the quantum geometry of the band, whose microscopic details may enhance or weaken ferromagnetism in moiré materials.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.1103/PHYSREVLETT.124.187601
