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

TL;DR

This study investigates how in-situ screening of disorder impacts fractional quantum Hall effects and composite fermion transport, revealing disorder broadening effects and disentangling impurity contributions using a dual-gate GaAs quantum well.

Contribution

It introduces an in-situ control method for disorder screening in quantum wells, enabling detailed analysis of disorder effects on FQHE and composite fermion properties.

Findings

Decreased screening increases disorder broadening and reduces FQHE energy gaps.

Resistivity at ν=1/2 correlates strongly with disorder broadening, not mobility.

Disentangling remote impurity and background impurity effects on resistivity.

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 $\nu = 1/2$. 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 ($n_\text{SL}$) of excess electrons in the modulation-doping superlattice. As the screening is reduced by decreasing $n_\text{SL}$ 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 $\Gamma$ of composite fermions (CFs). Interestingly, the increase in $\Gamma$ is accompanied by a noticeable increase in the longitudinal resistivity at $\nu = 1/2$ ($\rho_{1/2}$), with a much stronger correlation with $\Gamma$ than electron mobility $\mu$ has. The in-situ control of RI screening enables us to disentangle the contributions of RIs and background impurities (BIs) to $\rho_{1/2}$, with the latter in good agreement with the CF theory. We construct a scaling plot that helps in estimating the BI contribution to $\rho_{1/2}$ for a given set of $n_{e}$ and $\mu$.