Designing spin-textured flat bands in twisted graphene multilayers via helimagnet encapsulation

Abstract

Twisted graphene multilayers provide tunable platforms to engineer flat bands and exploit the associated strongly correlated physics. The two-dimensional nature of these systems makes them suitable for encapsulation by materials that break specific symmetries. In this context, recently discovered two-dimensional helimagnets, such as the multiferroic monolayer NiI${}_2$, are specially appealing for breaking time-reversal and inversion symmetries due to their nontrivial spin textures. Here we show that this spin texture can be imprinted on the electronic structure of twisted bilayer graphene by proximity effect. We discuss the dependence of the imprinted spin texture on the wave-vector of the helical structure, and on the strength of the effective local exchange field. Based on these results we discuss the nature of the superconducting instabilities that can take place in helimagnet encapsulated twisted bilayer graphene. Our results put forward helimagnetic encapsulation as a powerful way of designing spin-textured flat band systems, providing a starting point to engineer a new family of correlated moire states.

6 pages, 5 figures, comments are welcome

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• Giant proximity exchange and flat Chern band in 2D magnet-semiconductor heterostructures
• Impurity-induced Friedel oscillations in altermagnets and $p$-wave magnets
• Extended magic phase in twisted graphene multilayers
• Coexistence of $p$-wave magnetism and superconductivity
• The fate of $p$-wave spin polarization in helimagnets with Rashba spin-orbit coupling
• Moire-enabled topological superconductivity in twisted bilayer graphene
• Controlling magnetic frustration in 1T-TaS${}_2$ via Coulomb engineered long-range interactions
• Electrical probe of spin-spiral order in quantum spin Hall/spin-spiral magnet van der Waals heterostructures