We have studied electron transport in two closely spaced, electrically
isolated, two-dimensional electron gases (2DEGs) using GaAs/AlGaAs do
uble quantum wells. A frictional drag voltage due to interlayer electr
on-electron (e-e) scattering is induced in one layer when a current is
passed through the other. We present new experimental data based on a
detailed carrier-density dependence of these e-e interactions. We hav
e shown, in particular, that the interlayer scattering rate is a funct
ion of the relative electron densities in thr layers, with a maximum s
cattering rats when the two carrier densities are matched.