Spontaneous Valley Spirals in Magnetically Encapsulated Twisted Bilayer Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Van der Waals heterostructures offer tunable properties for emergent phenomena.
• Twisted bilayer graphene exhibits unique electronic characteristics.
• Ferromagnetic insulators provide magnetic proximity effects.

Purpose of the Study:

• To investigate the electronic band structure of twisted bilayer graphene interfaced with ferromagnetic insulators.
• To explore the role of twist angle, exchange proximity, and spin-orbit coupling.
• To understand interaction-induced phenomena and magnetic ordering in these systems.

Main Methods:

• Theoretical modeling of twisted bilayer graphene on ferromagnetic insulators.
• Analysis of electronic band structure considering twist, exchange, and spin-orbit coupling.
• Derivation of low-energy models for interaction-driven phenomena.

Main Results:

• Discovery of flat electronic bands in twisted bilayer graphene due to combined effects.
• Identification of valley degeneracy and description via a triangular superlattice model.
• Observation of spontaneous valley correlations favoring spiral order at half filling.
• Derivation of a valley-Heisenberg model with tunable exchange couplings.
• Demonstration of electric bias effect on band broadening and coupling tunability.

Conclusions:

• Magnetic van der Waals heterostructures are promising platforms for emergent physics.
• These systems facilitate the exploration of valley-correlated electronic states.
• Tunable flat bands and magnetic ordering offer new avenues for quantum material research.