Proximity screening greatly enhances electronic quality of graphene

TL;DR

Proximity screening using graphite gates dramatically improves graphene's electronic quality by reducing charge inhomogeneity and enabling high quantum mobilities, thus facilitating the observation of quantum phenomena at very low magnetic fields.

Contribution

Introducing a novel proximity screening technique with graphite gates that significantly enhances graphene's electronic quality and quantum transport properties.

Findings

Charge inhomogeneity reduced by two orders of magnitude.

Quantum mobility surpasses 10^7 cm^2/Vs, exceeding semiconductor heterostructures.

Fractional quantum Hall states remain observable despite screening.

Abstract

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 10$^8$ and 10$^6$ cm$^2$/Vs, respectively. Although the quality of graphene devices has also been improving, it remains comparatively lower. 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 10$^7$ cm$^-2$ and limiting potential fluctuations to less than 1 meV. Quantum mobilities reach 10$^7$ cm$^2$/Vs, surpassing those in the highest-quality semiconductor heterostructures by an order of magnitude, and the transport mobilities match their record. This quality enables Shubnikov-de Haas oscillations in fields as low as 1 mT and quantum Hall plateaus 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 to 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.