Imaging hydrodynamic electron flow in graphene with nitrogen vacancy centers in diamond

Strongly-interacting electronic systems feature transport that resembles the flow of a hydrodynamic fluid. Viscosity of such electron transport can lead to novel flow patterns, such as Poiseulle flow and vortices. Recent experiments in graphene and other materials provide evidence for such phenomena via electrical measurements. Here, we describe progress towards imaging hydrodynamic current flow in graphene via measurements of the associated stray magnetic field using nitrogen vacancy (NV) centers in diamond. An encapsulated graphene device is fabricated on a diamond. A dense ensemble of near-surface NVs, located beneath the graphene, serves as a local magnetic field sensor. The NV spin states are read out via their fluorescence and imaged onto a camera, revealing the local magnetic field pattern. We obtain high-resolution images of the stray-field generated by current flow in graphene, from which we reconstruct the pattern of electron flow. From these current maps we elucidate the effects of electron viscosity on local electron flow, which are otherwise difficult to access via traditional electrical measurements.