  The concept of fluidic viscosity is ubiquitous in our everyday life and for
it to arise the fluidic medium must necessarily form a continuum where
macroscopic properties can emerge. While a powerful concept for tangible
liquids, hydrodynamic manifestation of collective flow in electronic systems
such as two-dimensional electron gases (2DEGs) has only been shown recently to
occur in graphene and GaAs/AlGaAs. Here, we present nonlocal electronic
transport measurements in concentric annular rings formed in high-mobility
GaAs/AlGaAs 2DEGs and the resulting data strongly suggest that viscous
hydrodynamic flow can occur far away from the source-drain current region. Our
conclusion of viscous electronic transport is further corroborated by
simulations of the Navier-Stokes equations that are found to be in agreement
with our measurements below 1K temperature. Most importantly, our work
emphasizes the key role played by viscosity via electron-electron (e-e)
interaction when hydrodynamic transport is restricted radially, and for which a
priori should not have played a major role.
