  We measure transport through a Ga[Al]As heterostructure at temperatures
between 0.1 K and 30 K. Increasing the temperature enhances the
electron-electron scattering rate and viscous effects in the two-dimensional
electron gas arise. To probe this regime we measure so-called vicinity voltages
and use a voltage-biased scanning tip to induce a movable local perturbation.
We find that the scanning gate images differentiate reliably between the
different regimes of electron transport. Our data are in good agreement with
recent theories for interacting electron liquids in the ballistic and viscous
regimes stimulated by measurements in graphene. However, the range of
temperatures and densities where viscous effects are observable in Ga[Al]As are
very distinct from the graphene material system.

Mesoscale and Nanoscale Physics