Probing local current fluctuations in graphene with NV magnetometry*

Nitrogen Vacancy (NV) color centers in diamond are sensitive nanoscale magnetometers. We use this sensor to measure local current fluctuations in a biased graphene device in the electron hydrodynamic regime. We observe an anomalous current noise signal that is much larger than expected from Johnson-Nyquist noise in both global electronic noise and local NV center measurements. Furthermore, this signal exhibits strong asymmetries as a function of current direction and charge carrier sign. The local nature of this measurement technique allows us to also measure the spatial variation of this signal along the length of the device. I will discuss possible mechanisms for this noise generation and compare qualitative differences between the global and local noise measurements.