Pinning modes of high-magnetic-field Wigner solids with controlled alloy disorder

For a series of samples with two-dimensional electron systems in dilute AlxGa1-xAs, with varying x from 0% to 0.85%, we survey the pinning mode resonances of Wigner solids at the low Landau filling termination of the fractional quantum Hall effect series. For all x studied, the pinning modes are present with frequencies fpk that are consistent with collective weak pinning. For x≥0.22% we find fpk vs B exhibits a rapid increase that is not present for x=0. We find the observed fpk is much smaller than values calculated with a simple Wigner solid model which neglects the effects of the disorder on the charge distribution of a carrier.