$nu=5/2$ Fractional Quantum Hall State in Low-Mobility Electron Systems: Different Roles of Disorder

TL;DR

This study demonstrates the emergence of a fractional quantum Hall state at filling factor 5/2 in low-mobility GaAs/AlGaAs quantum wells, highlighting the roles of disorder and impurity screening in its formation and energy gap size.

Contribution

It shows that a 5/2 fractional quantum Hall state can form in low-mobility systems through impurity screening, revealing the impact of disorder on the energy gap.

Findings

Fractional quantum Hall state observed at ν=5/2 in low-mobility samples.

Energy gap Δ_{5/2} limited to ~100 mK despite improved transport.

Screening of remote impurity potential facilitates 5/2 state emergence.

Abstract

We report the observation of a fully developed fractional quantum Hall state at $\nu=5/2$ in GaAs/Al$_{x}$Ga$_{1-x}$As quantum wells with mobility well below $10^{7}$\thinspace cm$^{2}$/Vs. This is achieved either by strong illumination or reducing the barrier Al composition without illumination. We explain both results in terms of screening of the ionized remote impurity (RI) potential by nearby neutral shallow donors. Despite the dramatic improvement in the transport features, the energy gap $\Delta_{5/2}$ is limited to a rather small value ($\sim100$ mK), which indicates that once the RI potential is well screened and the $5/2$ state emerges, the size of $\Delta_{5/2}$ is limited by the mobility, i.e., by background impurities.