Quantum Hall effect at 0.002 T in graphene

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 $10^{7}c{m}^2{V}^{-1}{s}^{-1}$ . Shubnikov-de Haas oscillations emerge at magnetic fields below 1 mT, while integer quantum Hall features are observed at 0.002 T. Furthermore, we identify a fractional quantum Hall plateau at a filling factor of $v_{\mathrm{tot}}=-10/3$ at 2 T. These results demonstrate the platform's suitability for investigating strongly correlated electronic phases in graphene-based heterostructures.