# Twist-angle dependence of electron correlations in moir\'e graphene bilayers

## TL;DR

This paper investigates how electron correlations in twisted bilayer graphene depend on the twist angle, revealing strong correlations near the magic angle and highlighting the influence of substrate screening and Coulomb interactions.

## Contribution

It provides a detailed atomistic calculation of Hubbard parameters and shows how substrate screening and Coulomb interactions modulate electron correlations with twist angle.

## Key findings

- Strong correlations occur near the magic angle.
- Screening effects significantly reduce electron correlations.
- Long-range Coulomb interactions explain experimental sensitivity.

## Abstract

Motivated by the recent observation of correlated insulator states and unconventional superconductivity in twisted bilayer graphene, we study the dependence of electron correlations on the twist angle and reveal the existence of strong correlations over a narrow range of twist-angles near the magic angle. Specifically, we determine the on-site and extended Hubbard parameters of the low-energy Wannier states using an atomistic quantum-mechanical approach. The ratio of the on-site Hubbard parameter and the width of the flat bands, which is an indicator of the strength of electron correlations, depends sensitively on the screening by the semiconducting substrate and the metallic gates. Including the effect of long-ranged Coulomb interactions significantly reduces electron correlations and explains the experimentally observed sensitivity of strong correlation phenomena on twist angle.