Independently Tunable Flat Bands and Correlations in a Graphene Double Moir\'e System

TL;DR

This paper explores a four-layer graphene system with two twisted bilayers, demonstrating independently tunable flat bands and weak interlayer correlations, revealing insights into correlated insulating states and their dependence on twist angles.

Contribution

The study introduces a double moiré system with four graphene layers showing independently tunable flat bands and weak interlayer correlations, advancing understanding of correlated states in complex moiré structures.

Findings

Two sets of spatially separated flat bands are observed.

Correlated insulating states are most robust near the magic angle.

Gapped states at neutrality are more stable at larger twist angles.

Abstract

We report on a double moir\'e system consisting of four graphene layers, where the top and bottom pairs form small-twist-angle bilayer graphene, and the middle interface has a large rotational mismatch. This system shows clear signatures of two sets of spatially separated flat bands associated with the top and bottom twisted bilayer graphene (TBG) subsystems, each independently tunable. Thermodynamic analysis reveals weak correlations between layers that allow the chemical potential to be measured as a function of carrier density for each constituent TBG. We find that correlated insulating states at integer number of electrons per moir\'e unit cell are most robust near magic angle, whereas gapped states at neutrality are more robust at larger twist angles.