Dresden 2020 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 28: Twisted Bilayer Graphene (joint session TT/HL)

TT 28.3: Talk

Tuesday, March 17, 2020, 14:30–14:45, HSZ 201

Skyrmion lattices in twisted bilayer graphene — •Thomas Bömerich, Lukas Heinen, and Achim Rosch — Institute for Theoretical Physics, University of Cologne, Germany

We investigate the groundstate properties of magnetic skyrmions in anomalous Quantum Hall (AQH) systems. In these systems, the topological charge density, which characterizes the winding of a skyrmion, is directly proportional to the electric charge density. Therefore magnetic skyrmions are electrically charged excitations stabilized by Coulomb interactions between each other. At finite densities the skyrmions form regular lattices and can be controlled by external gate voltages. Our theory can be applied to twisted bilayer graphene as there is experimental evidence of ferromagnetic order and an AQH effect at specific fillings.

Starting from a free energy functional, we solve some limiting cases analytically and use micromagnetic simulations to study the lattice structure as a function of skyrmion density and skyrmion radius. From this we obtain a phase diagram with different skyrmion lattices. In particular we analyse the groundstate and its symmetries without external magnetic field. Additionally, we calculate the total magnetization as a function of skyrmion density, which can be used to detect experimental signatures of skyrmions in AQH systems.