Flat-band ferromagnetism in twisted bilayer graphene
We discuss twisted bilayer graphene (TBG) based on a theorem of flat-band ferromagnetism put forward by Mielke and Tasaki. According to this theorem, ferromagnetism occurs if the single-particle density matrix of the flat-band states is irreducible and we argue that this result can be applied to the...
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| Main Authors: | , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
1 December 2020
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| In: |
Physical review
Year: 2020, Volume: 102, Issue: 23 |
| ISSN: | 2469-9969 |
| DOI: | 10.1103/PhysRevB.102.235101 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1103/PhysRevB.102.235101 Verlag, lizenzpflichtig, Volltext: https://link.aps.org/doi/10.1103/PhysRevB.102.235101 
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| Author Notes: | R. Pons, A. Mielke, T. Stauber |
| Summary: | We discuss twisted bilayer graphene (TBG) based on a theorem of flat-band ferromagnetism put forward by Mielke and Tasaki. According to this theorem, ferromagnetism occurs if the single-particle density matrix of the flat-band states is irreducible and we argue that this result can be applied to the quasi-flat-bands of TBG that emerge around the charge-neutrality point for twist angles around the magic angle θ∼1.05∘. We show that the density matrix is irreducible in this case, thus predicting a ferromagnetic ground state for neutral TBG (n=0). We then show that the theorem can also be applied only to the flat conduction or valence bands, if the substrate induces a single-particle gap at charge neutrality. Also in this case, the corresponding density matrix turns out to be irreducible, leading to ferromagnetism at half filling (n=±2). |
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| Item Description: | Gesehen am 02.02.2021 |
| Physical Description: | Online Resource |
| ISSN: | 2469-9969 |
| DOI: | 10.1103/PhysRevB.102.235101 |