Flat-band ferromagnetism in twisted bilayer graphene

• Verfasst von: Pons, Rebecca [VerfasserIn]
• Verfasst von: Mielke, Andreas [VerfasserIn]
• Verfasst von: Stauber, Tobias [VerfasserIn]
• Titel: Flat-band ferromagnetism in twisted bilayer graphene
• Verf.angabe: R. Pons, A. Mielke, T. Stauber
• E-Jahr: 2020
• Jahr: 1 December 2020
• Fussnoten: Gesehen am 02.02.2021
• Titel Quelle: Enthalten in: Physical review
• Ort Quelle: Woodbury, NY : Inst., 2016
• Jahr Quelle: 2020
• Band/Heft Quelle: 102(2020,23) Artikel-Nummer 235101, 9 Seiten
• ISSN Quelle: 2469-9969
• DOI: doi:10.1103/PhysRevB.102.235101
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1746737441

Abstract

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).