Proximity screening greatly enhances electronic quality of graphene

The electronic quality of two-dimensional systems is crucial when exploring quantum transport phenomena. In semiconductor heterostructures, decades of optimization have yielded record-quality two-dimensional gases with transport and quantum mobilities reaching close to 10⁸ and 10⁶ cm² V^-1 s^-1, respectively^1-10. Although the quality of graphene devices has also been improving, it remains comparatively lower^11-17. Here we report a transformative improvement in the electronic quality of graphene by employing graphite gates placed in its immediate proximity, at 1 nm separation. The resulting screening reduces charge inhomogeneity by two orders of magnitude, bringing it down to a few 10⁷ cm^-2 and limiting potential fluctuations to less than 1 meV. Quantum mobilities reach 10⁷ cm² V^-1 s^-1, surpassing those in the highest-quality semiconductor heterostructures by an order of magnitude, and the transport mobilities match their record^9,10. This quality enables Shubnikov-de Haas oscillations in fields as low as 1 mT and quantum Hall plateaux below 5 mT. Although proximity screening predictably suppresses electron-electron interactions, fractional quantum Hall states remain observable with their energy gaps reduced only by a factor of 3-5 compared with unscreened devices, demonstrating that many-body phenomena at spatial scales shorter than 10 nm remain robust. Our results offer a reliable route to improving electronic quality in graphene and other two-dimensional systems, which should facilitate the exploration of new physics previously obscured by disorder.