Andreas Mielke
Institut für Theoretische Physik
Ruprecht-Karls Universität
Philosophenweg 19
D-69120 Heidelberg
Germany
Tel.: ++49 6221 549431 (Sekretariat)
Fax: ++49 6221 549331
e-mail: mielke@tphys.uni-heidelberg.de

### Archiv: arXiv:2007.04076

#### 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 $\theta\sim1.05^\circ$. 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 ($n=\pm2$).

#### BibTeX-Eintrag

@article{Pons2020,
author="Rebecca Pons, Andreas Mielke, Tobias Stauber",
title="Flat-band ferromagnetism in twisted bilayer graphene",
journal="Phys. Rev. B",
volume="102",
pages="235101",
year="2020"
}


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Letzte Änderung: 20.3.2022. mielke@tphys.uni-heidelberg.de
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