Inter-valley spiral order in the Mott insulating state of a heterostructure of trilayer graphene-boron nitride

TL;DR

This paper models the Mott insulating state in a trilayer graphene-boron nitride Moire super-lattice, revealing that inter-valley scattering induces a spiral order with a charge gap, explaining the observed insulating behavior.

Contribution

It introduces a valley-contrasting chiral tight-binding model and identifies inter-valley spiral order as the origin of Mott insulation in this system.

Findings

Valley-contrasting staggered flux around π/2

Perfect nesting of Fermi surfaces between valleys

Inter-valley scattering induces a charge gap and spiral order

Abstract

Recent experiment has shown that the ABC-stacked trilayer graphene-boron nitride Moire super-lattice at half-filling is a Mott insulator. Based on symmetry analysis and effective band structure calculation, we propose a valley-contrasting chiral tight-binding model with local Coulomb interaction to describe this Moire super-lattice system. By matching the positions of van Hove points in the low-energy effective bands, the valley-contrasting staggered flux per triangle is determined around $\pi /2$. When the valence band is half-filled, the Fermi surfaces are found to be perfectly nested between the two valleys. Such an effect can induce an inter-valley spiral order with a gap in the charge excitations, indicating that the Mott insulating behavior observed in the trilayer graphene-boron nitride Moire super-lattice results predominantly from the inter-valley scattering.