Dresden 2020 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 28: Twisted Bilayer Graphene (joint session TT/HL)
TT 28.4: Talk
Tuesday, March 17, 2020, 14:45–15:00, HSZ 201
Magnetism of magic-angle twisted bilayer graphene — •Javad Vahedi1,2, Andreas Honecker2, Robert Peters3, and Guy Trambly de Laissardière2 — 1Institut für Mathematische Physik, Technische Universität Braunschweig, Germany — 2Laboratoire de Physique Théorique et Modélisation, Université de Cergy-Pontoise, France — 3Department of Physics, Kyoto University, Japan
Recently, correlated insulators and superconductivity have been discovered experimentally in twisted bilayer graphene (TBG) [1]. The Moiré pattern of the bilayers at so-called “magic angles” leads to localization of the low-energy electrons in the AA-stacking regions, reflected by very flat regions in the band structure [2]. This reduction of the kinetic energy enhances the relative importance of interactions and thus renders the bilayer systems much more susceptible to correlation effects than a single layer. We investigate the magnetic instabilities at half filling in TBG using a real-space Hartree-Fock and RPA analysis. We find that at charge neutrality an antiferromagnetic state localized in the AA region emerges for values of the Coulomb interaction U that are an order of magnitude smaller than what would be required to render an antiferromagnetic state in a single graphene sheet. Furthermore, doping of a few electrons per Moiré unit cell pushes the system into a ferromagnetic phase.
[1] Y. Cao et al., Nature 556, 80 (2018); Nature 556, 43 (2018)
[2] G. Trambly de Laissardière et al., Nano Letters 10, 804 (2010)