  In sufficiently clean materials where electron-electron interactions are
strong compared to momentum-relaxing scattering processes, electron transport
resembles the flow of a viscous fluid. We study hydrodynamic electron transport
across density interfaces (n-n junctions) in a 2DEG in the Corbino geometry.
From numerical simulations in COMSOL using realistic parameters, we show that
we can produce tunable viscous layers at the density interface by varying the
density ratio of charge carriers. We quantitatively explain this observation
with simple analytic expressions together with boundary conditions at the
interface. We also show signatures of these viscous layers in the
magnetoresistance. Breaking down viscous and ohmic contributions, we find that
when outer radial region of the Corbino has higher charge density compared to
the inner region, the viscous layers at the interface serve to suppress the
magneto-resistance produced by momentum-relaxing scattering. Conversely, the
magneto-resistance is enhanced when the inner region has higher density than
the outer. Our results add to the repertoire of techniques for engineering
viscous electron flows, which hold a promise for applications in future
electronic devices.
