Tuesday, June 25, 2013

1306.5290 (J. Shabani et al.)

Phase Diagrams for the Stability of the ν= 1/2 Fractional Quantum
Hall Effect in Wide GaAs Quantum Wells

J. Shabani, Y. Liu, M. Shayegan, L. N. Pfeiffer, K. W. West, K. W. Baldwin
We report an experimental investigation of the unique fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor \nu = 1/2 in very high quality wide GaAs quantum wells, and at very high magnetic fields up to 35 T. The quasi-two-dimensional electron systems we study are confined to GaAs quantum wells with widths W ranging from 44 to 96 nm, and have bilayer-like, symmetric charge distributions and variable densities in the range of $\simeq 4 \times 10^{11}$ to $\simeq 4 \times 10^{10}$ cm$^{-2}$. We present several experimental phase diagrams for the stability of the \nu=1/2 FQHE in these quantum wells. First, for a given W, the 1/2 FQHE is stable in a limited range of intermediate densities; it makes a transition to a compressible phase at low densities and to an insulating phase at high densities. The densities at which the \nu=1/2 FQHE is stable are larger for narrower quantum wells. Second, we present a plot of the symmetric-to-antisymmetric subband separation ($\Delta_{SAS}$), which characterizes the inter-layer tunneling, vs density for various W. This plot reveals that $\Delta_{SAS}$ at the boundary between the compressible and FQHE phases increases linearly with density. Finally, we summarize the experimental data in a diagram that takes into account the relative strengths of the inter-layer and intra-layer Coulomb interactions and $\Delta_{SAS}$. We conclude that, consistent with the conclusions of previous studies, the \nu=1/2 FQHE observed in wide GaAs quantum wells with symmetric charge distribution is likely a two-component state.
View original: http://arxiv.org/abs/1306.5290

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