# Regensburg 2022 – wissenschaftliches Programm

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# MM: Fachverband Metall- und Materialphysik

## MM 28: Transport in Materials: Diffusion / Electrical Transport & Magnetism

### MM 28.3: Vortrag

### Donnerstag, 8. September 2022, 10:45–11:00, H44

**Non-coplanar magnetism, topological density wave order and emergent symmetry at half-integer filling of moiré Chern bands** — •Patrick Wilhelm^{1}, Thomas Lang^{1}, Mathias Scheurer^{1}, and Andreas Läuchli^{1,2,3} — ^{1}Institut für Theoretische Physik, Universität Innsbruck, 6020 Innsbruck, Austria — ^{2}Laboratory for Theoretical and Computational Physics, Paul Scherrer Institute, 5232 Villigen, Switzerland — ^{3}Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland

We study the impact of Coulomb interactions at half-integer filling of the moiré Chern bands of twisted double-bilayer graphene and twisted mono-bilayer graphene, using unbiased exact diagonalization comple-mented by unrestricted Hartree-Fock calculations. For small intra-sublattice tunneling, wAA, a non-coplanar magnetic state is found which has the same symmetries as the tetrahedral antiferromagnet of the triangular moiré lattice and can be thought of as a skyrmion lattice commensurate with the moiré scale. The antiferromagnetic order competes with a set of ferromagnetic, topological charge density waves, which are favored for larger wAA and are associated with an approximate emergent O(3) symmetry, 'rotating' the different charge density wave states into each other. Exhibiting a finite charge gap and Chern number C=|1|, the formation of charge density wave order which is intimately connected to a skyrmion lattice phase is consistent with recent experiments on these systems.