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We examine the impact of random potential due to remote impurites (RIs) andits in-situ controlled screening on fractional quantum Hall effects (FQHEs)around Landau-level filling factor $\nu = 1/2$. The experiment is made possibleby using a dual-gate GaAs quantum well (QW) that allows for the independentcontrol of the density $n_{e}$ of the two-dimensional electron system in the QWand that ($n_\text{SL}$) of excess electrons in the modulation-dopingsuperlattice. As the screening is reduced by decreasing $n_\text{SL}$ at afixed $n_{e}$, we observe a decrease in the apparent energy gap of the FQHEsdeduced from thermal activation, which signifies a corresponding increase inthe disorder broadening $\Gamma$ of composite fermions (CFs). Interestingly,the increase in $\Gamma$ is accompanied by a noticeable increase in thelongitudinal resistivity at $\nu = 1/2$ ($\rho_{1/2}$), with a much strongercorrelation with $\Gamma$ than electron mobility $\mu$ has. The in-situ controlof RI screening enables us to disentangle the contributions of RIs andbackground impurities (BIs) to $\rho_{1/2}$, with the latter in good agreementwith the CF theory. We construct a scaling plot that helps in estimating the BIcontribution to $\rho_{1/2}$ for a given set of $n_{e}$ and $\mu$.

Impact of in-situ controlled disorder screening on fractional quantum Hall effects and composite-fermion transport