Spin-Polarization of Composite Fermions and Particle-Hole Symmetry Breaking

We study the critical spin-polarization energy ($α_{\rm C}$) above which fractional quantum Hall states in two-dimensional electron systems confined to symmetric GaAs quantum wells become fully spin-polarized. We find a significant decrease of $α_{\rm C}$ as we increase the well-width. In systems with comparable electron layer thickness, $α_{\rm C}$ for fractional states near Landau level filling $ν=3/2$ is about twice larger than those near $ν=1/2$, suggesting a broken particle-hole symmetry. Theoretical calculations, which incorporate Landau level mixing through an effective three-body interaction, and finite layer thickness, capture certain qualitative features of the experimental results.

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