Ruprecht-Karls-Universität Heidelberg
University of HeidelbergFaculty of Physics and AstronomyInstitut of Theoretical PhysicsAndreas MielkeAndreas Mielkeemail

Andreas Mielke
Institut for Theoretical Physics
Ruprecht-Karls University
Philosophenweg 19
D-69120 Heidelberg
Germany
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e-mail: mielke@tphys.uni-heidelberg.de


Rebecca Pons, Andreas Mielke, Tobias Stauber: Flat-band ferromagnetism in twisted bilayer graphene
Phys. Rev. B102, 235101 (2020) .

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-entry

@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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Last changes: 2.9.2024. mielke@tphys.uni-heidelberg.de
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