Dirac points, spinons and spin liquid in twisted bilayer graphene

Understand

Twisted bilayer graphene is an excellent example of highly correlated system demonstrating a nearly flat electron band, the Mott transition and probably a spin liquid state.

• Besides the one-electron picture, analysis of Dirac points is performed in terms of spinon Fermi surface in the limit of strong correlations.
• Application of gauge field theory to describe deconfined spin liquid phase is treated.
• Topological quantum transitions, including those from small to large Fermi surface in the presence of van Hove singularities, are discussed.