Scattering of otherwise ballistic electrons far from equilibrium is
investigated in a cold two-dimensional electron system. The interaction between
excited electrons and the degenerate Fermi liquid induces a positive charge in
a nanoscale region which would be negatively charged for diffusive transport at
local thermal equilibrium. In a three-terminal device we observe avalanche
amplification of electrical current, resulting in a situation comparable to the
Venturi effect in hydrodynamics. Numerical calculations using a random phase
approximation are in agreement with our data and suggest Coulomb interaction as
the dominant scattering mechanism.Comment: 4 pages, 4 figure
