Graphene enables precise carrier-density control via gating, making it an ideal platform for studying electronic interactions. However, sample inhomogeneities often limit access to the low-density regimes where these interactions dominate. Enhancing carrier mobility is therefore crucial for exploring fundamental properties and developing device applications. Here, we demonstrate a significant reduction in external inhomogeneity using a double-layer graphene architecture separated by an ultra-thin hexagonal boron nitride layer. Mutual screening between the layers reduces scattering from random Coulomb potentials, resulting in a quantum mobility exceeding. Shubnikov de-Haas oscillations emerge at magnetic fields below 1 mT, while integer quantum Hall features are observed at 0.002T. Furthermore, we identify a fractional quantum Hall plateau at a filling factor of at 2T. These results demonstrate the platform's suitability for investigating strongly correlated electronic phases in graphene-based heterostructures.
@article{arxiv.2601.16015,
title = {Quantum Hall Effect at 0.002T},
author = {Alexander S. Mayorov and Ping Wang and Xiaokai Yue and Biao Wu and Jianhong He and Di Zhang and Fuzhuo Lian and Siqi Jiang and Jiabei Huang and Zihao Wang and Qian Guo and Kenji Watanabe and Takashi Taniguchi and Renjun Du and Rui Wang and Baigeng Wang and Lei Wang and Kostya S. Novoselov and Geliang Yu},
journal= {arXiv preprint arXiv:2601.16015},
year = {2026}
}