Abstract
We examine the impact of random potential due to remote impurites (RIs) and its in-situ controlled screening on fractional quantum Hall effects (FQHEs) around Landau-level filling factor ν = 1/2. The experiment is made possible by using a dual-gate GaAs quantum well (QW) that allows for the independent control of the density n_e of the two-dimensional electron system in the QW and that (nSL) of excess electrons in the modulation-doping superlattice. As the screening is reduced by decreasing nSL at a fixed n_e, we observe a decrease in the apparent energy gap of the FQHEs deduced from thermal activation, which signifies a corresponding increase in the disorder broadening Γ of composite fermions (CFs). Interestingly, the increase in Γ is accompanied by a noticeable increase in the longitudinal resistivity at ν = 1/2 (ρ_1/2), with a much stronger correlation with Γ than electron mobility μ has. The in-situ control of RI screening enables us to disentangle the contributions of RIs and background impurities (BIs) to ρ_1/2, with the latter in good agreement with the CF theory. We construct a scaling plot that helps in estimating the BI contribution to ρ_1/2 for a given set of n_e and μ.