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

TL;DR

This paper proposes using helimagnet encapsulation to induce spin textures in twisted graphene multilayers, enabling the engineering of flat bands and correlated states with potential superconducting instabilities.

Contribution

It introduces a novel method of imprinting spin textures onto twisted graphene via helimagnet proximity, opening new avenues for designing correlated moire systems.

Findings

Spin textures can be imprinted on twisted graphene by helimagnet proximity.

The spin texture depends on the helimagnet wave-vector and exchange field strength.

Helimagnetic encapsulation offers a new way to engineer spin-textured flat bands.

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.