Milli-Tesla Quantization enabled by Tuneable Coulomb Screening in Large-Angle Twisted Graphene

TL;DR

This paper demonstrates that tuning Coulomb screening in large-angle twisted graphene encapsulation significantly reduces charge fluctuations, enabling ultra-sensitive electronic measurements at very low magnetic fields.

Contribution

The study introduces a novel encapsulation method using large-angle twisted graphene layers to enhance electronic quality through tunable Coulomb screening.

Findings

Landau quantization observed at ~5 mT

Reduced charge inhomogeneity to a few carriers per μm²

Resolved small energy gap at the Dirac point

Abstract

The electronic quality of graphene has improved significantly over the past two decades, revealing novel phenomena. However, even state-of-the-art devices exhibit substantial spatial charge fluctuations originating from charged defects inside the encapsulating crystals, limiting their performance. Here, we overcome this issue by assembling devices in which graphene is encapsulated by other graphene layers while remaining electronically decoupled from them via a large twist angle (~10-30{\deg}). Doping of the encapsulating graphene layer introduces strong Coulomb screening, maximized by the sub-nanometer distance between the layers, and reduces the inhomogeneity in the adjacent layer to just a few carriers per square micrometre. The enhanced quality manifests in Landau quantization emerging at magnetic fields as low as ~5 milli-Tesla and enables resolution of a small energy gap at the Dirac point. Our encapsulation approach can be extended to other two-dimensional systems, enabling further exploration of the electronic properties of ultrapure devices.