The interplay of strong correlations and topology in 2D moiré materials

• Applicant: Dr. Timo Gräßer
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570240234

After the discovery of graphene and other two-dimensional (2D) systems of atomic thickness, the possibility of engineering novel materials through the combination of 2D layers arose. A major breakthrough happened in 2018 with the discovery of gate-tunable superconductivity and correlated insulating states in magic-angle twisted bilayer graphene, two stacked layers of graphene with a relative rotation angle of about 1 degree, opening the fields of twistronics and moiré materials. Stacking two similar, but non-identical lattices creates a moiré pattern with a very large unit cell, which alters the electronic structure of the material and controls its properties. Combining different 2D materials with different moiré realizations opens endless possibilities for the design of quantum materials and the discovery of novel quantum states. Since 2018, an incredible variety of quantum phases and phenomena have been found in twisted bilayer graphene and other moiré materials. A thorough understanding of the nature and phenomenology of the quantum states in these materials is still lacking. Central ingredients are the formation of very narrow electronic bands, which are highly sensitive to electronic interactions, as well as unconventional topological properties, which non-trivially affect the formation of local moments. The effective microscopic descriptions depend on the specific moiré geometry and the chemical composition. Using advanced dynamical mean-field theory, this project aims at thoroughly understanding the quantum states which emerge in moiré materials due to the interplay between electronic correlations and topology. The primary focus lies on the moiré materials magic-angle twisted bilayer graphene and AB-stacked MoTe2/WSe2, which both can be effectively described by topological heavy-fermion models.

• DFG Programme: WBP Fellowship
• International Connection: Spain
• Host: Dr. Elena Bascones Fernández de V