Spatial measurements of ballistic and hydrodynamic signatures in Graphene

The study of electric current, dominated by electron-electron interactions, has recently gained interest owing to a new generation of ultra clean materials. In this regime, the flow behaves as viscous hydrodynamics fluid, in contrast to non-interacting flow types such as diffusive and ballistic. In this work, we use a scanning single electron transistor (SET) to image the local potential landscape produced by flowing electrons in an expanding channel of graphene. This geometry is ideal to reveal the spatial manifestation of the quantum contact resistance as well as non-local aspects of ballistic and hydrodynamic flows. In this talk we will present our recent scanning measurements that shed new light on all the above aspects of electron flow.