Nanoscale electronic transport gives rise to a number of intriguing physical phenomena that are accompanied by distinct spatial patterns of current flow. Here, we report on sensitive magnetic imaging of two-dimensional current distributions in bilayer graphene at room temperature. By combining dynamical modulation of the source-drain current with ac quantum sensing of a nitrogen-vacancy center in a diamond probe, we acquire magnetic field and current density maps with excellent sensitivities of 4.6 nT and 20 nA/μm, respectively. The spatial resolution is 50-100 nm. We further introduce a set of methods for increasing the technique's dynamic range and for mitigating undesired back-action of magnetometry operation on the electronic transport. Current density maps reveal local variations in the flow pattern and global tuning of current flow via the back-gate potential. No signatures of hydrodynamic transport are observed. Our experiments demonstrate the feasibility for imaging subtle features of nanoscale transport in two-dimensional materials and conductors.
@article{arxiv.2201.06934,
title = {Imaging of sub-$\mu$A currents in bilayer graphene using a scanning diamond magnetometer},
author = {M. L. Palm and W. S. Huxter and P. Welter and S. Ernst and P. J. Scheidegger and S. Diesch and K. Chang and P. Rickhaus and T. Taniguchi and K. Wantanabe and K. Ensslin and C. L. Degen},
journal= {arXiv preprint arXiv:2201.06934},
year = {2022}
}