Imaging of sub-$\mu$A currents in bilayer graphene using a scanning diamond magnetometer

TL;DR

This study demonstrates sensitive magnetic imaging of sub-microampere currents in bilayer graphene at room temperature using a diamond magnetometer, revealing detailed current flow patterns and local variations.

Contribution

It introduces a novel method combining ac quantum sensing with dynamical current modulation for high-resolution magnetic imaging of nanoscale currents in 2D materials.

Findings

Achieved magnetic field sensitivity of 4.6 nT and current density sensitivity of 20 nA/μm.

Resolved current flow patterns with 50-100 nm spatial resolution.

No evidence of hydrodynamic transport in bilayer graphene under studied conditions.

Abstract

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/$\mu$m, 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.