Phase diagrams for the stability of the fractional quantum Hall effect in electron systems confined to symmetric, wide GaAs quantum wells

Abstract

We report an experimental investigation of the fractional quantum Hall effect (FQHE) at the even-denominator Landau-level filling factor ν=1/2 in very-high-quality wide GaAs quantum wells and at very high magnetic fields up to 45 T. The quasi-two-dimensional electron systems we study are confined to GaAs quantum wells with widths W ranging from 41 to 96 nm and have variable densities in the range of â‰4×1011 to â‰4×1010 cm-2. We present several experimental phase diagrams for the stability of the ν=1/2 FQHE in these quantum wells. In general, for a given W, the 1/2 FQHE is stable in a limited range of intermediate densities where it has a bilayerlike charge distribution; it makes a transition to a compressible phase at low densities and to an insulating phase at high densities. The densities at which the ν=1/2 FQHE is stable are larger for narrower quantum wells. Moreover, even a slight charge distribution asymmetry destabilizes the ν=1/2 FQHE and turns the electron system into a compressible state. We also present a plot of the symmetric-to-antisymmetric subband separation (ΔSAS),which characterizes the interlayer tunneling, vs density for various W. This plot reveals that ΔSAS at the boundary between the compressible and FQHE phases increases linearly with density for all the samples. There is no theoretical explanation for such a simple dependence. Finally, we summarize the experimental data in a diagram that takes into account the relative strengths of the interlayer and intralayer Coulomb interactions and ΔSAS. We conclude that consistent with the conclusions of some of the previous studies, the ν=1/2 FQHE observed in wide GaAs quantum wells with symmetric charge distribution is stabilized by a delicate balance between the interlayer and intralayer interactions and is very likely described by a two-component (Ψ331) state.