  We present a gating scheme to separate even strong parallel conductance from
the magneto-transport signatures and properties of a two-dimensional electron
system. By varying the electron density in the parallel conducting layer, we
can study the impact of mobile charge carriers in the vicinity of the dopant
layer on the properties of the two-dimensional electron system. It is found
that the parallel conducting layer is indeed capable to screen the remote
ionized impurity potential fluctuations responsible for the fragility of
fractional quantum Hall states.
