# Strong Electronic Correlation Originates from the Synergistic Effect of Large Moir\'e Cell and Strong Interlayer Coupling in Twisted Graphene Bilayer

## TL;DR

This study reveals that strong electronic correlations in twisted bilayer graphene arise from the combined effects of large Moiré cell size and strong interlayer coupling, as shown through first-principles calculations.

## Contribution

It demonstrates how tuning Moiré cell size and interlayer spacing can induce strongly correlated electronic states in twisted bilayer graphene.

## Key findings

- Electronic correlation increases with larger Moiré cells.
- Stronger interlayer coupling enhances electronic correlation.
- Correlated states can be achieved with band widths less than 0.01 eV.

## Abstract

By using the first-principles method based on density of functional theory, we study the electronic properties of twisted bilayer graphene with some specific twist angles and interlayer spacings. With the decrease of the twist angle(the unit cell becomes larger), the energy band becomes narrower and Coulomb repulsion increases, leading to the enhancement of electronic correlation; On the other hand, as the interlayer spacing decreases and the interlayer coupling becomes stronger, the correlation becomes stronger. By tuning the interlayer coupling, we can realize the strongly correlated state with the band width less than 0.01 eV in medium-sized Moir\'e cell of twisted bilayer graphene. These results demonstrate that the strength of electronic correlation in twisted bilayer graphene is closely related to two factors: the size of unit cell and the distance between layers. Consequently, a conclusion can be drawn that the strong electronic correlation in twisted bilayer graphene originates from the synergistic effect of the large size of Moir\'e cell and strong interlayer coupling on its electronic structure.